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  • Articles  (107)
  • methane  (106)
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  • Atomic, Molecular and Optical Physics
  • Chemical Engineering
  • Springer  (107)
  • 2000-2004  (21)
  • 1995-1999  (85)
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  • Chemistry and Pharmacology  (106)
  • Philosophy  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Parametric Study of a Pressure Swing Adsorption Process (2000)
    Springer
    Adsorption 6 (2000), S. 179-188 
    Details
    ISSN: 1572-8757
    Keywords: pressure swing adsorption ; methane ; hydrogen ; process design
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The performance of a pressure swing adsorption (PSA) process for production of high purity hydrogen from a binary methane-hydrogen mixture is simulated using a detailed, adiabatic PSA model. An activated carbon is used for selective adsorption of methane over hydrogen. The effects of various independent process variables (feed gas pressure and composition, purge gas pressure and quantity, configuration of process steps) on the key dependent process variables (hydrogen recovery at high purity, hydrogen production capacity) are evaluated. It is demonstrated that many different combinations of PSA process steps, their operating conditions, and the feed gas conditions can be chosen to produce an identical product gas with different hydrogen recovery and productivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008925703871
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  • 2
    Electronic Resource
    Electronic Resource
    Carbon dioxide reforming of methane to synthesis gas over hexaaluminate ANiAl11O19-delta (A = Ca, Sr, Ba and La) catalysts (2000)
    Springer
    Catalysis letters 64 (2000), S. 157-161 
    Details
    ISSN: 1572-879X
    Keywords: hexaaluminate ANiAl11O19-δ catalysts ; methane ; CO2 reforming ; synthesis gas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A series of A‐modified hexaaluminates, ANiAl11O19-δ (A = Ca, Sr, Ba and La) as new catalysts for carbon dioxide reforming of methane to synthesis gas, were prepared by decomposition of nitrates and calcination at high temperature. Nickel ions as active component were inlayed in the hexaaluminate lattices to substitute part of Al ions. The structure and properties of these samples were characterized using XRD, XPS, TPR and TGA techniques. The series of hexaaluminates exhibited significantly catalytic activity and stability at high temperature, for instance at 780°C for 18 h, the conversion of CH4 and CO2 was kept over 91.0 and 93.7%, respectively, meanwhile no Ni sintering, phase transformation and catalyst deactivation due to carbon deposition were found. Besides, the modifier A in the mirror plane layer of the lattices showed different effects on reducibility and catalytic activity of transition metal Ni in the hexaaluminate lattices.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019039004361
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  • 3
    Electronic Resource
    Electronic Resource
    Formation of C m H n (m ≥ 3, n ≤ m) hydrocarbons from C1 and C2 molecules by high‐temperature (≥1000°C), short‐contact‐time (1–10 ms) nozzle beam reactions (2000)
    Springer
    Catalysis letters 64 (2000), S. 85-93 
    Details
    ISSN: 1572-879X
    Keywords: methane ; ethane ; acetylene ; benzene ; longer chain hydrocarbons ; supersonic nozzle beam ; contact time ; reaction order
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A nozzle, fabricated from nickel, molybdenum, iron, palladium, and quartz was utilized to produce longer chain hydrocarbons, C m H n (m ≥ 3, n≤ m) from C2 (ethane, acetylene) and C1 (methane) reactants at nozzle temperature range 1000–1150°C. The conversion of ethane was close to 100% at T noz = 1000°C, while that of methane reached 20% at T noz = 1150°C. The contact time in the nozzle is in the 10-3–10-2 s range. The reactions are first and higher order in reactant pressure. The reaction mechanism involves the formation of free radicals at the nozzle surface followed by gas‐phase reactions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019032330286
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  • 4
    Electronic Resource
    Electronic Resource
    Steady-state conversion of methane to C4+ aliphatic products in high yields using an integrated recycle reactor system (2000)
    Springer
    Catalysis letters 66 (2000), S. 1-4 
    Details
    ISSN: 1572-879X
    Keywords: methane ; oxidation ; aliphatic hydrocarbons ; zeolite ; recycle reactor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Conversion of methane in high yields to C4+ nonaromatic hydrocarbons was demonstrated in a recycle system. The principal components of the recycle system included an oxidative coupling reactor with a Mn/Na2WO4/SiO2 catalyst at 800°C for conversion of methane to ethylene, and a reactor with an H-ZSM-5 zeolite at 275°C for subsequent conversion of ethylene to higher hydrocarbons. Total yields of C4+ products were in the range of 60–80%, and yields of C4+ nonaromatic hydrocarbons were in the range of 50–60%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019039321142
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  • 5
    Electronic Resource
    Electronic Resource
    Isothermal, non‐oxidative, two‐step CH4 conversion over unsupported and supported Ru and Pt catalysts (2000)
    Springer
    Catalysis letters 66 (2000), S. 113-120 
    Details
    ISSN: 1572-879X
    Keywords: ruthenium ; platinum ; methane ; non‐oxidative ; two‐step conversion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The isothermal, non‐oxidative, two‐step conversion of CH4 to C2+ hydrocarbons was investigated over unsupported and supported Pt and Ru catalysts at moderate temperatures and elevated pressures. The single‐cycle specific activity (µmol C2+/gcat) and total product yield (µmol C2+/µmol surface metal) for Ru powder at 430 K were significantly higher than for Pt powder at 503 K. The activity and total product yield for mixed metal oxide (MMO)‐supported Ru were significantly less than for Ru powder; however, Pt/MMO exhibited similar activity and product yield in comparison to Pt powder. The formation of methylbutane and methylpentane increased with increasing pressure over Ru/MMO. However, increasing pressure favored the formation of C4 species over Pt/MMO.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019064026593
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  • 6
    Electronic Resource
    Electronic Resource
    Development of a novel test system for in situ catalytic, electrocatalytic and electrochemical studies of internal fuel reforming in solid oxide fuel cells (2000)
    Springer
    Catalysis letters 66 (2000), S. 221-226 
    Details
    ISSN: 1572-879X
    Keywords: solid oxide fuel cells ; electrocatalysis ; catalysis ; electrochemistry ; anode ; fuel reforming ; steam reforming ; methane ; carbon deposition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A test system based around a thin‐walled extruded solid electrolyte tubular reactor has been developed, which enables the fuel reforming catalysis and surface chemistry occurring within solid oxide fuel cells and the electrochemical performance of the fuel cell to be studied under genuine operating conditions. It permits simultaneous monitoring of the catalytic chemistry and the cell performance, allowing direct correlation between the fuel cell performance and the reforming characteristics of the anode, as well as enabling the influence of drawing current on the catalysis and surface reaction pathways to be studied. Temperature‐programmed reaction measurements can be carried out on anodes in an actual SOFC, and have been used to investigate the reduction characteristics of different anode formulations, methane activation and methane steam reforming, and to evaluate the nature and level of carbon deposition on the anode during reforming.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019024312481
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  • 7
    Electronic Resource
    Electronic Resource
    Role of the surface state of Ni/Al2O3 in partial oxidation of CH4 (2000)
    Springer
    Catalysis letters 67 (2000), S. 139-145 
    Details
    ISSN: 1572-879X
    Keywords: methane ; partial oxidation ; syngas ; Ni/Al2O3 ; gas phase O2 ; adsorbed oxygen species ; surface state
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The effect of gas phase O2 and reversibly adsorbed oxygen on the decomposition of CH4 and the surface state of a Ni/Al2O3 catalyst during partial oxidation of CH4 were studied using the transient response technique at atmospheric pressure and 700°C. The results show that, when the catalyst surface is completely oxidized under experimental conditions, only a small amount of CO and H2 can be produced from non‐selective oxidation of CH4 by reversibly adsorbed oxygen which is more active in oxidizing CH4 completely than NiO via the Rideal–Eley mechanism and both the conversions of CH4 and O2 and the selectivities to CO and H2 are very low. Therefore, keeping the catalyst surface in the reduced state is the precondition of high conversion of CH4 and high selectivities to CO and H2. The surface state of the catalyst decides the reaction mechanism and plays a very important role in the conversions and selectivities of partial oxidation of CH4. During partial oxidation of CH4, no oxygen species but a small amount of carbon exists on the catalyst surface, which is favorable for maintaining the catalyst in the reduced state and the selectivity of CO. The results also indicate that direct oxidation is the main route for partial oxidation of CH4, and the indirect oxidation mechanism is not able to gain dominance in the reaction under the experimental conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019025807455
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  • 8
    Electronic Resource
    Electronic Resource
    In situ DRIFTS study of NO reduction with CH4 over PtCo-ferrierite catalysts (2000)
    Springer
    Catalysis letters 68 (2000), S. 169-174 
    Details
    ISSN: 1572-879X
    Keywords: emission control ; nitrogen oxides ; selective catalytic reduction ; methane ; DRIFTS ; PtCo-ferrierite
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The effect of platinum incorporated into Co-ferrierite catalyst on the selective catalytic reduction of NOx with CH4 was studied by means of in situ DRIFTS technique. NO adsorption on Co- and PtCo-ferrierite catalysts gave dinitrosyl and mononitrosyl species on Co2+ ions. The adsorption of NO + O2 on Co-ferrierite yielded NO2 (NO 2 δ +) species and also nitrites and nitrates. Similar species were observed on PtCo-ferrierite, although chemisorbed NO2 was much more stable since it persisted at reaction temperatures as high as 723 K. The spectra of the pre-reduced bimetallic PtCo-ferrierite catalyst exposed to the CH4 + NO + O2 reaction mixture showed bands at 2200–2100 cm-1, which were similar to results for a Pt-free sample but slightly more intense. In addition, strong bands of nitrate, almost unchanged with temperature, were observed. A very stable Co2+–NO2 intermediate species was developed upon incorporation of Pt into the base Co-ferrierite catalyst.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019043706063
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  • 9
    Electronic Resource
    Electronic Resource
    Methane partial oxidation by silica‐supported iron phosphate catalysts. Influence of iron phosphate content on selectivity and catalyst structure (2000)
    Springer
    Topics in catalysis 10 (2000), S. 115-122 
    Details
    ISSN: 1572-9028
    Keywords: selective oxidation ; methane ; methanol ; formaldehyde ; iron phosphate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Selective oxidation of methane to methanol and formaldehyde at atmospheric pressure was studied over a series of silica‐supported FePO4 catalysts, with iron phosphate content ranging from 2 to 16 wt%. Performance was evaluated over the range T=773–963 K, GHSV=25,000–65,000 h−1, and CH4 : O2=1. The main products were formaldehyde, carbon monoxide and carbon dioxide. Small, but quantifiable amounts of methanol were also observed. Catalytic activity exhibited a clear dependence on the iron phosphate content. The highest selectivity and space time yield (STY) to formaldehyde and methanol were observed for 2 wt% FePO4 on silica (STY of 622 and 25 g/kgcat h, respectively). The selectivity–conversion pattern suggests that methane is oxidized directly to methanol and formaldehyde, and sequentially to carbon oxides. Characterization was performed by X‐ray powder diffraction, X‐ray photoelectron spectroscopy, and Mössbauer spectroscopy. Crystalline FePO4 is observed at all loading levels, however, a significant fraction of the iron (58% at 2 wt% FePO4) is present in an X‐ray amorphous phase. Mössbauer spectra suggest that this phase contains iron in five‐fold coordination, and with a higher electron density relative to bulk FePO4. The amount of this five‐coordinate phase present is roughly 1 wt% Fe, independent of total iron loading. XPS confirms the lower effective oxidation state of iron, and indicates that at low loading the surface is enriched in phosphorus relative to bulk FePO4. It is proposed that iron in five‐fold coordinate sites, isolated by phosphate groups, more selectively activates methane than crystalline FePO4. As loading increases, so does the amount of crystalline FePO4, which is proposed to more rapidly catalyze sequential oxidation of the selective products.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019120218882
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  • 10
    Electronic Resource
    Electronic Resource
    Methane activation by surface oxygen in calcia-stabilized zirconia (2000)
    Springer
    Catalysis letters 68 (2000), S. 203-208 
    Details
    ISSN: 1572-879X
    Keywords: redox ; methane ; calcia–zirconia ; transient kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Methane activation at 450–700°C by 14 mol% calcia-stabilized zirconia was studied by the transient reaction of pure methane with the oxidized material. Three distinct sequential reaction regimes are observed. Initially, methane oxidation rates are similar to those in cofed methane–oxygen mixtures. After a small amount of oxygen (amount) is removed from the material, the reactivity of the material suddenly increases while a larger amount of oxygen, roughly equivalent to 1 surface layer, is removed. Finally, after this reductive phase, methane continues to react rapidly to deposit a surface layer of carbonaceous material which can be removed by reoxidation. This cycle can be repeated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019060209697
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  • 11
    Electronic Resource
    Electronic Resource
    Role of iron and copper in particulate methane monooxygenase of Methylosinus trichosporium OB3b (2000)
    Springer
    Catalysis surveys from Japan 4 (2000), S. 51-63 
    Details
    ISSN: 1572-8803
    Keywords: particulate methane monooxygenase ; methanotrophs ; Methylosinus trichosporium OB3b ; methane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The role of iron and copper in particulate methane monooxygenase (pMMO) of Methylosinus trichosporium OB3b is described, and an overview of the enzyme's properties is presented. The pMMO from M. trichosporium OB3b was solubilized in the detergent n-dodecyl-β-D-maltoside and purified by chromatographic techniques. The enzyme consists of 0.9 iron atoms and 12.8 copper atoms per molecule. The iron site in pMMO may be mononuclear non-heme iron. Copper exists as either copper ion coupled to four nitrogen atoms and/or trinuclear copper cluster wherein copper ions are ferromagnetically coupled.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019036105038
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  • 12
    Electronic Resource
    Electronic Resource
    Methane conversion by various metal, metal oxide and metal carbide catalysts (2000)
    Springer
    Catalysis surveys from Japan 4 (2000), S. 3-15 
    Details
    ISSN: 1572-8803
    Keywords: methane ; conversion ; metal ; metal oxide ; metal carbide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The progress in the field of methane conversion into higher hydrocarbons including aromatics and oxygenated compounds in the recent five years will be reviewed shortly, together with a new type of the methane conversion reaction with carbon monoxide at lower temperatures (600–700 K) by supported group VIII metal catalysts. Benzene was formed selectively among hydrocarbons in the CH4–CO reaction over silica-supported Rh, Ru, Pd and Os catalysts under atmospheric pressure. Both CH4 and CO were required for benzene formation, and only ethane and ethylene were formed besides benzene. The amount of C3–C5 hydrocarbons was negligible, which suggests that a completely different mechanism from the CO–H2 reaction may be operating over these catalysts despite of the similarity in the reaction conditions with the CO–H2 reaction. The mechanism of benzene formation was studied deeply by means of kinetical investigation as well as infrared spectroscopy and isotopic tracer method in connection with that of CO hydrogenation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019084020968
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  • 13
    Electronic Resource
    Electronic Resource
    A Plasma-Activated Ni/α-Al2O3 Catalyst for the Conversion of CH4 to Syngas (2000)
    Springer
    Plasma chemistry and plasma processing 20 (2000), S. 137-144 
    Details
    ISSN: 1572-8986
    Keywords: plasma-activation ; nickel-based catalyst ; methane ; partial oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Nickel-based catalysts supported on α-Al2O3 for the partial oxidationof methane were activated by a glow discharge plasma technique. Theactivating process was simple, quick, audio-visual, and easy to control. Theactivity and stability of the activated catalyst were higher than those ofconventional catalysts. The methane conversion of 98.2% and selectivity of97.3% to hydrogen and 96.5% to carbon monoxide were obtained at850°C. The catalyst could maintain its activity over 15 hr. According tothe results of X-ray diffraction (XRD) and temperature-programmed reduction(TPR), the component of crystal phase and the reducibility of the activatedcatalyst were significantly different from those of conventionalcatalysts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006978012228
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  • 14
    Electronic Resource
    Electronic Resource
    On the contribution of X-ray absorption spectroscopy to explore structure and activity relations of Pt/ZrO2 catalysts for CO2/CH4 reforming (2000)
    Springer
    Topics in catalysis 10 (2000), S. 295-305 
    Details
    ISSN: 1572-9028
    Keywords: XAFS ; carbon dioxide ; methane ; synthesis gas ; platinum ; zirconia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract X-ray absorption spectroscopy (XAS) has proven to be a very useful technique in characterizing metal-based catalysts exposed to extreme operating conditions. The technique allows in situ evaluation of structural parameters (XAFS) and electronic properties (XANES). The elucidation of the nature and state of Pt-based catalysts in dry reforming of methane with carbon dioxide is presented as case study to show the contribution and potential of XAS to explore property/performance relationships for heterogeneous catalysts. Pt/ZrO2 is an active and stable catalyst for the reaction between CH4 and CO2 to synthesis gas (H2/CO). The activity and stability of the catalyst is strongly influenced by the catalyst pretreatment (calcination/reduction). The combination of hydrogen chemisorption, IR spectroscopy, XPS and XAS is shown to be suitable to track the changes of the state of the catalyst. In particular, it will be demonstrated, how XAFS helped to correctly attribute variations in the chemisorptive properties of Pt/ZrO2 after severe temperature treatment to partial and reversible decoration of the small Pt particles with fragments of the oxide support. In situ tracking of the reduction of the catalysts by XANES additionally helped to semiquantitatively assess the partial reduction of the ZrO2. Finally, XANES helped to demonstrate that CO2 exposure under these severe conditions did not lead to detectable levels of surface oxidation of Pt. Based on XANES, IR spectroscopy and kinetic measurements it is concluded that in dry reforming activation of methane occurs on Pt, while CO2 is activated on the support and the two entities react at the metal–support interface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019149025242
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  • 15
    Electronic Resource
    Electronic Resource
    ESR Study of the Plasma Polymerizations of Trimethylsilane and Methane (2000)
    Springer
    Plasmas and polymers 5 (2000), S. 235-253 
    Details
    ISSN: 1572-8978
    Keywords: ESR ; plasma polymerization ; free radical ; thin films ; trimethylsilane ; methane ; PE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Electron Spin Resonance (ESR) was used to study, at the molecular level, the plasma polymerization of trimethylsilane (TMS) and methane. Direct ESR analysis of the plasma coated Al substrate required the use of a novel ESR technique. TMS plasma deposit on Al showed a single broad resonance line near g = 2.003. The signal was stable in vacuum and decayed on exposure to air, with a significant fraction persisting for days. Results show that this signal arises from silicon dangling bonds. Identical TMS signals were observed from films prepared by the DC cathodic or the AF glow discharge method but their decay rates were different. In contrast, the deposition of methane produced two distinct types of carbon-based signals depending upon the method of deposition. TMS or CH4 films deposited by the DC cathodic method showed slow signals decay and high refractive indices value. While the use of Al as the substrate showed plasma-coating radicals, only substrate radicals were observed when PE was used as the substrate. The nature of radicals formed depends not only on the deposition method used but also on the substrate type.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1011377900516
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  • 16
    Electronic Resource
    Electronic Resource
    Fluxes of methane and carbon dioxide from a small productive lake to the atmosphere (2000)
    Springer
    Biogeochemistry 49 (2000), S. 1-19 
    Details
    ISSN: 1573-515X
    Keywords: carbon dioxide ; diffusion ; ebullition ; emission ; freshwater ; hypertrophic lakes ; methane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The fluxes of CH4 and CO2 to the atmosphere, and the relative contributions of ebullition and molecular diffusion, were determined for a small hypertrophic freshwater lake (Priest Pot, UK) over the period May to October 1997. The average total flux of CH4 and CO2 (estimated from 7 sites on the lake) was approximately 52 mmol m−2 d−1 and was apportioned 12 and 40 mmol m−2 d−1 toCH4 and CO2 respectively. Diffusion across the air-water interface accounted for the loss of 0.4and 40 mmol m−2 d−1 of CH4 and CO2 respectively whilst the corresponding figures for ebullition losses were 12.0 (CH4) and 0.23 (CO2) mmol m−2 d−1. Most CH4 (96%) was lost by ebullition, and most CO2 (99%) by diffusive processes. The ebullition of gas, measured at weekly intervals along a transect of the lake, showed high spatial and temporal variation. The CH4 content of the trapped gas varied between 44 and 88% (by volume) and was highest at the deepest points. Pulses of gas ebullition were detected during periods of rapidly falling barometric pressure. Therelevance of the measurements to global estimates ofcarbon emission from freshwaters are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006269900174
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  • 17
    Electronic Resource
    Electronic Resource
    Dynamics of dissolved O2, CO2, CH4, and N2O in a tropical coastal swamp in southern Thailand (2000)
    Springer
    Biogeochemistry 49 (2000), S. 191-215 
    Details
    ISSN: 1573-515X
    Keywords: carbon dioxide ; coastal peat swamp ; methane ; nitrous oxide ; oxygen ; pyrite oxidation ; redox condition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We studied the distribution of dissolved O2, CO2, CH4, and N2O in a coastal swamp system in Thailand with the goal to characterize the dynamics of these gases within the system. The gas concentrations varied spatially and seasonally in both surface and ground waters. The entire system was a strong sourcefor CO2 and CH4, and a possible sink for atmospheric N2O. Seasonal variation in precipitation primarily regulated the redox conditions in the system. However, distributions of CO2, CH4, and N2O in the river that received swamp waters were not always in agreement with redox conditions indicated by dissolvedO2 concentrations. Sulfate production through pyriteoxidation occurred in the swamp with thin peat layerunder aerobic conditions and was reflected by elevatedSO 4 2− /Cl− in the river water. When SO 4 2− /Cl− was high, CO2 and CH4 concentrations decreased, whereas the N2O concentration increased. The excess SO 4 2− in the river water was thus identified as a potential indicator for gas dynamics in this coastal swamp system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006393214432
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  • 18
    Electronic Resource
    Electronic Resource
    Methane turnover in exposed sediments of an Amazon floodplain lake (2000)
    Springer
    Biogeochemistry 50 (2000), S. 195-206 
    Details
    ISSN: 1573-515X
    Keywords: methane ; Amazon ; floodplain ; sediments
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract In the Amazon floodplain large areas of unvegetatedlake sediments are exposed to air during low water. Imeasured methane fluxes from exposed sediments of anAmazonian floodplain lake and assessed the regulatingfactors. Methane emission decreased from values between 10 and 40 μmol CH4 mminus 2 hminus 1to zero when the sediments were exposed to air. Meanfluxes were about 3.7 μmol CH4mminus 2 hminus 1. Fluxes were low compared tomeasurements taken from flooded habitats makingexposed lake sediments a negligible source ofatmospheric CH4. This was mainly due to the lackof ebullition which governs methane flux in theflooded phase. Methane oxidation at the sedimentsurface consumed up to 75% of the methane enteringthe oxidised zone. Compared with CO2 emissionmethane turnover was of minor importance for thecarbon budget of the sediments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006326018597
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  • 19
    Electronic Resource
    Electronic Resource
    Catalytic Removal of NOx from Gas Mixtures Simulating Emissions from the Combustion of Biofuels (2000)
    Springer
    Reaction kinetics and catalysis letters 70 (2000), S. 17-25 
    Details
    ISSN: 1588-2837
    Keywords: Biofuels ; nitrogen oxides ; methane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The activity of knitted silica-fibre supported Pd, Pt, Pt-Ni, Pd-Ni and Pd-Pt-Ni catalysts as well as Pd based H-ZSM-5 and H-ZSM-35 catalysts was studied in the conversion of gas mixtures containing 200 ppm CH4, 2500 ppm CO, 500 ppm pyridine (or 500 ppm NO), 10 vol.% O2 (or 0.155 vol.% O2), 12 vol.% CO2, 12 vol.% H2O, balanced with He at GHSV of 60000 h−1. Pyridine was found to inhibit both CO and CH4 oxidation. IR studies indicated that NO adsorbed on Pd2+ is the principal adsorbed species on the Pd/HZSM-5 catalyst.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1010342127680
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  • 20
    Electronic Resource
    Electronic Resource
    Methane Conversion Over Sr2+/La2O3 Catalyst Modified with Nickel and Copper (2000)
    Springer
    Reaction kinetics and catalysis letters 69 (2000), S. 145-152 
    Details
    ISSN: 1588-2837
    Keywords: Catalysis ; methane ; lanthanum oxide ; stronlium ; nickel ; copper
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Methane transformation over Ni and Cu modified Sr2+/La2O3 catalysts has been studied. These species favor formation of reducible mixed oxides and change the surface reactivity of the Sr2+/La2O3 system, modifying the reaction mechanism, since Sr2+/La2O3 favors methane oxidative coupling but with copper methane combustion is favored and nickel favors partial oxidation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005617515362
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    Kinetics of the Selective Reduction of NO with CH4 Over an In-Fe2O3/HZSM-5 Catalyst (2000)
    Springer
    Reaction kinetics and catalysis letters 69 (2000), S. 299-303 
    Details
    ISSN: 1588-2837
    Keywords: Kinetics ; In-Fe2O3/HZSM-5 ; nitrogen oxide ; selective reduction ; methane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A kinetic model presented for the selective reduction of NO with CH4 over an In-Fe2O3/HZSM-5 catalyst by considering the process as a combination of two simultaneous reactions: NO+O2+CH4 (reaction 1) and O2+CH4 (reaction 2). Linear regression calculation was employed to find the kinetic parameters. It was found that although the activation energies of the two reactions were almost identical, the reaction rate constants were dramatically different, namely, k1≫k2, indicating that the NO+O2+CH4 reaction was more preferable to take place on the In-Fe2O3/HZSM-5 catalyst as compared with the O2+CH4 reaction.
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    URL: http://dx.doi.org/10.1023/A:1005651900767
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    Synergistic effects in the oxidation of methane on strontium and lead hydroxyapatites (1999)
    Springer
    Catalysis letters 57 (1999), S. 161-165 
    Details
    ISSN: 1572-879X
    Keywords: methane ; oxidation ; strontium hydroxyapatite ; lead hydroxyapatite ; tetrachloromethane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The oxidation of methane has been investigated on lead hydroxyapatite (PbHAp), strontium hydroxyapatite (SrHAp) and their binary mixtures at 873 K. PbHAp showed no activity for the oxidation of methane, while SrHAp produced carbon monoxide selectively at 2–4% conversion. On binary mixtures of the hydroxyapatites the conversion of methane and the selectivity to C2 compounds reached values higher than those of the separate constituents of the mixture. With tetrachloromethane in the feed stream a similar synergistic effect was observed with conversions of methane and selectivities to CH3Cl higher on the binary mixtures than those on either SrHAp or PbHAp. The strontium-containing hydroxyapatite appears to play a crucial role in the activation of methane, while the presence of the lead-containing analogue is apparently required for the minimization of undesirable processes involving methyl radicals.
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    URL: http://dx.doi.org/10.1023/A:1019024421857
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    Novel rhenium‐based catalysts for dehydrocondensation of methane with CO/CO2 towards ethylene and benzene (1999)
    Springer
    Catalysis letters 62 (1999), S. 29-33 
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    ISSN: 1572-879X
    Keywords: methane ; dehydrocondensation ; benzene ; ethylene ; Re catalyst ; HZSM‐5
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A new family of rhenium‐based catalysts bearing HZSM‐5 zeolite exhibits remarkable performances for the catalytic dehydrocondensation of methane with CO/CO2 towards ethylene, benzene, and naphthalene in high selectivity of above 90% at 1–3 atm and 973–1023 K. In contrast to Mo/HZSM‐5 catalysts, the EXAFS and TG/DTA/Mass studies reveal that the metallic Re on HZSM‐5 zeolite is a catalytically active and stable phase for the reaction.
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    URL: http://dx.doi.org/10.1023/A:1019022316715
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    A study of “superacidic” MoO3/ZrO2 catalysts for methane oxidation (1999)
    Springer
    Catalysis letters 57 (1999), S. 109-113 
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    ISSN: 1572-879X
    Keywords: superacid ; zirconia ; molybdenum oxide ; methane ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A series of zirconia-supported molybdenum oxide catalysts with different molybdenum loadings prepared using conditions reported to generate “superacidity” have been evaluated for their performance as catalysts for methane oxidation. A marked dependence of Mo content on activity has been observed, with the most active material being that with intermediate molybdenum content. 5 wt% MoO3/ZrO2 compares favourably with ZrxCe1-xO2 for methane combustion. The presence of MoO3 is observed to stabilise the tetragonal polymorph of ZrO2 and, as Mo content is increased, dispersed MoO3 crystallites are formed as evidenced by Raman spectroscopy. Temperature-programmed reduction studies evidence differences in the reduction behaviour of the materials as a function of loading. The results indicate that molybdenum oxide supported on monoclinic zirconia gives rise to the most active catalyst. It is tentatively suggested that the formation of a MoO3 monolayer during reaction may be of importance.
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    URL: http://dx.doi.org/10.1023/A:1019047632335
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    Comparison of the group V and VI transition metal carbides for methane dry reforming and thermodynamic prediction of their relative stabilities (1999)
    Springer
    Catalysis letters 57 (1999), S. 65-69 
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    ISSN: 1572-879X
    Keywords: methane ; synthesis gas ; dry reforming ; transition metal carbides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The group V and VI transition metal carbides have been prepared by CH4 TPR, and tested for the dry reforming of methane with carbon dioxide, at elevated pressure. Mo2C and WC were the most stable catalysts, while the group V metal carbides showed the stability order: vanadium $${\text{ 〉}}$$ niobium $${\text{ 〉}}$$ tantalum. Catalyst deactivation was due to carbide oxidation with CO2, while stability was associated with the reaction of metal oxide (from deactivation) with CH4, giving the metal carbide. Calculation of the Gibbs free energy for this reaction resulted in a predicted catalyst stability trend similar to that obtained experimentally.
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    URL: http://dx.doi.org/10.1023/A:1019062608228
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    Methane conversion over sulfated zirconia (1999)
    Springer
    Catalysis letters 58 (1999), S. 123-125 
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    ISSN: 1572-879X
    Keywords: methane ; sulfated zirconia ; ethene ; isobutane ; superacid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In a continuous-flow differential microreactor, sulfated zirconia (SZ), deliberately activated in situ by water, has converted methane at 673 K to a C2–C6 hydrocarbon mixture of which 65–70% was ethene and isobutane. Maximum conversion activity of ∼4.6%, corresponding to 4×104 mole methane reacted per mole sulfate per second, was attainable at S/(added H2O) molar ratio of 3.0 and methane flow rate of 5.6×106 mol (g-SZ)−1 s−1. This methane conversion could be catalytic and may involve superacidic sites.
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    URL: http://dx.doi.org/10.1023/A:1019021715922
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    Characteristics of methane combustion over La–Cr–O catalysts (1999)
    Springer
    Catalysis letters 58 (1999), S. 63-66 
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    ISSN: 1572-879X
    Keywords: La–Cr–O catalyst ; methane ; combustion ; oxygen adsorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The catalytic activities of methane combustion of La–Cr–O catalysts prepared with and without polyacrylic acid as a template have been compared. The polymer-templated catalyst had a higher BET surface area, 12.3 m2 g−1, than that obtained from the conventional precipitation method, 2.9 m2 g−1. The results of XRD and SEM experiments suggested that the structural characteristics were almost similar. Surprisingly, the areal rate of methane combustion over the catalyst with a small surface area was ten times larger than that of the catalyst with a large surface area. However, the site time yields (STY) based on the oxygen adsorption capacity were similar, independent of the surface area and preparation conditions.
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    URL: http://dx.doi.org/10.1023/A:1019092809562
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    Pure and Binary Gas Adsorption Equilibria and Kinetics of Methane and Nitrogen on 4A Zeolite by Isotope Exchange Technique (1999)
    Springer
    Adsorption 5 (1999), S. 145-158 
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    ISSN: 1572-8757
    Keywords: kinetics ; isotope-exchange ; nitrogen ; adsorption ; methane ; zeolite ; equilibria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The Isotope Exchange Technique (IET) was used to simultaneously measure pure and binary gas adsorption equilibria and kinetics (self-diffusivities) of CH4 and N2 on pelletized 4A zeolite. The experiment was carried out isothermally without disturbing the adsorbed phase. CH4 was selectively adsorbed over N2 by the zeolite because of its higher polarizability. The multi-site Langmuir model described the pure gas and binary adsorption equilibria fairly well at three different temperatures. The selectivity of adsorption of CH4 over N2 increased with increasing pressure at constant gas phase composition and temperature. This curious behavior was caused by the differences in the sizes of the adsorbates. The diffusion of CH4 and N2 into the zeolite was an activated process and the Fickian diffusion model described the uptake of both pure gases and their mixtures. The self-diffusivity of N2 was an order of magnitude larger than that for CH4. The pure gas self-diffusivities for both components were constants over a large range of surface coverages (0 〈 θ 〈 0.5). The self-diffusivities of CH4 and N2 from their binary mixtures were not affected by the presence of each other, compared to their pure gas self-diffusivities at identical surface coverages.
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    URL: http://dx.doi.org/10.1023/A:1008917308002
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    Combustion of a trace amount of CH4 in the presence of water vapor over ZrO2-supported Pd catalysts (1999)
    Springer
    Catalysis letters 58 (1999), S. 127-130 
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    ISSN: 1572-879X
    Keywords: combustion ; methane ; palladium catalyst ; zirconia ; water vapor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Combustion of a trace amount of CH4 over Pd catalysts supported on calcined ZrO2 was examined under nearly exhaust gas conditions where the temperature is not so high and water vapor coexists. High catalytic activity was obtained with ZrO2 support calcined at 1073 and 1273 K. The durability test at 673 K for 100 h revealed that the activity of these catalysts hardly decreased, while that of the Pd catalysts supported on calcined Al2O3 were much decreased in the course of time. These results demonstrated the advantages of ZrO2 as a support for Pd catalysts in the present reaction.
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    URL: http://dx.doi.org/10.1023/A:1019030017739
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    The effect of oxygen on the aromatization of methane over the Mo/HZSM‐5 catalyst (1999)
    Springer
    Catalysis letters 63 (1999), S. 73-77 
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    ISSN: 1572-879X
    Keywords: methane ; oxygen ; aromatization ; Mo/HZSM‐5 ; coke formation ; UV‐Raman spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The aromatization of methane over a Mo/HZSM‐5 catalyst was carried out in the presence of oxygen. It is shown that the addition of a small amount of oxygen is beneficial to improve the durability of the catalyst. UV‐Raman spectra disclose that the carbonaceous deposits formed on the HZSM‐5 are mainly polyolefinic and aromatic, while that on the Mo/HZSM‐5 is mainly polyaromatic. The small amount of O2 added may partly remove the coke deposits on the active sites and keep the catalyst as MoOxCy/HZSM‐5, thus resulting in an improvement of the catalytic performance of the Mo/HZSM‐5 catalyst.
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    URL: http://dx.doi.org/10.1023/A:1019096300302
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    Coherent Anti-Stokes Raman Scattering Applied to Hydrocarbons in a Microwave Excited Process Plasma (1999)
    Springer
    Plasma chemistry and plasma processing 19 (1999), S. 91-109 
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    ISSN: 1572-8986
    Keywords: Microwave plasma ; CARS on methyl ; methane ; hydrogen ; modeling, methane plasma ; electron energy distribution function
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Coherent anti-Stokes Raman scattering (CARS) carried out using the BOXCARS technique is applied to quantify the density and temperature of hydrogen, methane, and methyl in a process plasma generated by a surfatron in the pressure range from 30 to 3000 Pa. Below approximately 500 Pa all species and their temperatures have a flat distribution dominated by diffusive processes. At higher pressure the plasma localizes near the inner surface of the surfatron tube. A strong depletion of the methane ground state density is observed, where the gas temperature remains at 400 K on a moderate level. On the other side the methyl density is high at the position of high methane depletion. The measured methyl density is a factor of 200 lower than the methane density, in contrast to the factor 10–20 often reported in the literature. The measured data can be interpreted by proper modeling by means of the Boltzmann equation of electrons, balancing of chemical reactions and diffusive processes. The calculated methane and methyl densities agree with the measured ones only if the electron temperature is assumed to be near 1 eV and thus much lower than predicted in previous papers.
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    URL: http://dx.doi.org/10.1023/A:1021808000636
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    Tunable Diode Laser Diagnostic Studies of H2-Ar-O2 Microwave Plasmas Containing Methane or Methanol (1999)
    Springer
    Plasma chemistry and plasma processing 19 (1999), S. 395-419 
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    ISSN: 1572-8986
    Keywords: Microwave plasma ; plasma chemistry ; methane ; methanol ; laser diagnostics ; TDLAS ; CH3 ; CH2O ; HCOOH
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Tunable infrared diode laser absorption spectroscopy has been used to detect the methyl radical and ten stable molecules in H2-Ar-O2 microwave plasmas containing up to 7.2% of methane or methanol, under both flowing and static conditions. The degree of dissociation of the hydrocarbons varied between 30 and 90% and the methyl radical concentration was found to be in the range 10 10 –10 12 molecules cm −3 . The methyl radical concentration and the concentrations of the stable C-2 hydrocarbons C 2 H 2 , C 2 H 4 , and C 2 H 6 , produced in the plasma decayed exponentially when increasing amounts of O 2 were added at fixed methane or methanol partial pressures. In addition to detecting the hydrocarbon species, the major products CO, CO 2 , and H 2 O were also monitored. For the first time, formaldehyde, formic acid, and methane were detected in methanol microwave plasmas, formaldehyde was detected in methane microwave plasmas. Chemical modeling with 57 reactions was used to successfully predict the concentrations in methane plasmas in the absence of oxygen and the trends for the major chemical product species as oxygen was added.
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    URL: http://dx.doi.org/10.1023/A:1021872420200
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    The CO2 Reforming of Natural Gas in a Pulsed Corona Discharge Reactor (1999)
    Springer
    Plasma chemistry and plasma processing 19 (1999), S. 505-512 
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    ISSN: 1572-8986
    Keywords: Corona discharge ; methane ; carbon dioxide ; carbon monoxide ; cold plasma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract The conversion of CO 2 and (CH 4+CO 2 ) mixtures to CO, at room temperature and atmospheric pressure conditions, in pulsed corona discharges, was investigated. Conversion of pure CO 2 was 16.8% at 10 cm 3 -min −1 flow rate, which corresponds to 75 μmol-min −1 rate of conversion. The CO 2 conversion was improved to 38% (85 μmol-min −1 by feeding the reactor with CH 4+CO 2 gas mixture (1:1 ratio), simultaneously with CH 4 conversion of 46% (∼102.7 μmol-min −1 ) at 10 cm 3 -min −1 flow rate of feed gases and 9 W power conditions. Rate of CO production is increased from ∼110 to ∼180 μmol-min −1 with the variation of feed gas (CH 4+CO 2 mixture, 1:1 ratio) flow rate from 10 to 40 cm 3 -min −1 at 9W, which corresponds to energy efficiency of 2.5 to 4.1%. Highest energy yield of 25 g/kWh for CH 4 conversion, 29 g/kWh for CO 2 conversion, and 33 g/kWh for CO production were achieved.
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    Ellipsometric study of a palladium catalyst during the oxidation of carbon monoxide and methane (1999)
    Springer
    Topics in catalysis 8 (1999), S. 35-43 
    Details
    ISSN: 1572-9028
    Keywords: ellipsometry ; carbon monoxide ; methane ; palladium ; palladium oxide ; oxidation ; oscillations ; catalyst
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Spectroscopic ellipsometry is used to monitor the surface of a thick Pd‐film catalyst during the oxidation of either carbon monoxide or methane. Dense PdO layers form under sufficiently lean conditions (excess oxygen) for both reactions. A stable metal surface exists in the case of CO, but a very porous PdO layer develops in the case of methane, under rich conditions. There is a large hysteresis in the conditions for PdO formation in the case of CO oxidation. Spontaneous oscillations in catalytic activity and Pd‐surface composition occur for both reactions, the higher activities corresponding to O‐atom‐rich or PdO‐rich surfaces for CO or methane oxidation, respectively.
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    CO2 reforming of methane over vanadia-promoted Rh/SiO2 catalysts (1999)
    Springer
    Topics in catalysis 8 (1999), S. 211-222 
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    ISSN: 1572-9028
    Keywords: reforming ; methane ; carbon dioxide ; Rh/SiO2 ; vanadia-promoted Rh/SiO2 ; FTIR spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The reforming of methane with carbon dioxide over rhodium dispersed on silica, Rh/SiO2, and vanadia-promoted silica, Rh/VOx/SiO2, was studied by kinetic test reactions under differential conditions in a temperature range from 723 to 773 K. Transmission infrared spectroscopy was applied to observe the interaction of CO2 with the catalysts and the formation of surface intermediates during the CO2–CH4 reforming reaction. To analyze carbon deposition XP spectroscopy and TPO was carried out. It has been shown that the promotion of Rh/SiO2 catalysts with vanadium oxide enhances the catalytic activity for CO2 reforming of methane and decreases the deactivation by carbon deposition. This is attributed to the formation of a partial VOx overlayer on the Rh surface, which reduces the size of accessible ensembles of Rh atoms required for coke formation and creates new sites at the Rh–VOx interfacial region that are considered to be active sites for the activation/dissociation of carbon dioxide.
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    C2 and C3 hydrocarbon gases associated with highly reducing conditions in groundwater (1999)
    Springer
    Biogeochemistry 47 (1999), S. 15-23 
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    ISSN: 1573-515X
    Keywords: ethane ; groundwater ; methane ; propane ; redox ; soil gas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract This study investigates the presence and concentration of light hydrocarbon gases in soil vapor located immediately above the capillary fringe of a petroleum-contaminated aquifer. A correlation was observed for the linear regression plot of redox potential versus detectable C2+C3 alkane concentrations for a limited number of sampling points. C2+C3 alkanes were not detected at points were redox potentials in groundwater exceeded --260 millivolts. The predominance of methanogenic processes in this redox range, as well as the observed C2+C3 concentration ratios, suggest that ethane and propane gases in soil vapor may be biogenically produced as well as a result of volatilization from NAPL.
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    URL: http://dx.doi.org/10.1023/A:1006147818047
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    C2 and C3 hydrocarbon gases associated with highly reducing conditions in groundwater (1999)
    Springer
    Biogeochemistry 47 (1999), S. 15-23 
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    ISSN: 1573-515X
    Keywords: ethane ; groundwater ; methane ; propane ; redox ; soil gas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract This study investigates the presence and concentration of light hydrocarbon gases in soil vapor located immediately above the capillary fringe of a petroleum-contaminated aquifer. A correlation was observed for the linear regression plot of redox potential versus detectable C2+C3 alkane concentrations for a limited number of sampling points. C2+C3 alkanes were not detected at points were redox potentials in groundwater exceeded -260 millivolts. The predominance of methanogenic processes in this redox range, as well as the observed C2+C3 concentration ratios, suggest that ethane and propane gases in soil vapor may be biogenically produced as well as a result of volatilization from NAPL.
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    URL: http://dx.doi.org/10.1007/BF00993094
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    Ethylene and methane in the upper water column of the subtropical Atlantic (1999)
    Springer
    Biogeochemistry 44 (1999), S. 73-91 
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    ISSN: 1573-515X
    Keywords: Atlantic ; ethylene ; methane ; sea-air exchange
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The vertical distributions of ethylene and methane in the upper water column of the subtropical Atlantic were measured along a transect from Madeira to the Caribbean and compared with temperature, salinity, oxygen, nutrients, chlorophyll-a, and dissolved organic carbon (DOC). Methane concentrations between 41.6 and 60.7 nL L−1 were found in the upper 20 m of the water column giving a calculated average flux of methane into the atmosphere of 0.82μg m−2 h−1. Methane profiles reveal several distinct maxima in the upper 500 m of the water column and short-time variations which are presumably partly related to the vertical migration of Zooplankton. Ethylene concentrations in near surface waters varied in the range of 1.8 to 8.2 nL L−1. Calculated flux rates for ethylene into the atmosphere were in the range of 0.41 to 1.35μg m−2 h−1 with a mean of 0.83μg m−2h−2. Maximum concentrations of up to 39.2 nL L−2 were detected directly below the pycnocline in the western Atlantic. The vertical distributions of ethylene generally showed one maximum at the pycnocline (about 100 m depth) where elevated concentrations of chlorophyll-a, dissolved oxygen, and nutrients were also found; no ethylene was detected below 270 m depth. This suggests that ethylene release is mainly related to one, probably phytoplankton associated, source, while for methane, enhanced net production occurs at various depth horizons. For surface waters, a simple correlation between ethylene and chlorophyll-a or DOC concentrations could not be observed. No considerable diurnal variation was observed for the distribution and concentration of ethylene in the upper water column.
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    Determinants of spatial variability of methane emissions from wet grasslands on peat soil (1999)
    Springer
    Biogeochemistry 44 (1999), S. 221-237 
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    ISSN: 1573-515X
    Keywords: grassland ; methane ; peat ; spatial variability ; wetland
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Methane (CH4) emissions from soils, representing the consequence of CH4 production, CH4 consumption and CH4 transport, are poorly characterised and show a large spatial variability. This study aimed to assess the determinants of field-scale spatial variability of CH4 emissions from wet grasslands on peat soil. Mean CH4 emission rates of a three-year experiment at 18 plots distributed over three sites in the nature preserve “Nieuwkoopse Plassen” on peat soil in the Netherlands were related to CH4 production and CH4 consumption capacities of soil layers, and to soil and vegetation characteristics. Spatial variability of CH4 emissions and possible determining factors was high. Annual CH4 emissions ranged from 3 to 37 g CH4 m-2 yr-1. Coefficients of variation (CV) of CH4 emissions were on average 37% among sites and 83% within sites. Most important determinants of spatial variability were CH4 production capacity (average: 211 ng CH4 g-1 dry soil h-1; CV: 131%) and aboveground biomass of sedges (Carex spp.) (average: 0.45 g dm-2; CV: 127%) (P 〈 0.01). Sedges may affect CH4 emissions by stimulating CH4 transport from anaerobic layers to the surface via their vascular system and/or by serving as substrate for methanogens. For extrapolation of CH4 emissions to larger areas, best results will be obtained by using factors that are easy to determine, like vegetation.
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    Methane emissions from wet grasslands on peat soil in a nature preserve (1999)
    Springer
    Biogeochemistry 44 (1999), S. 205-220 
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    ISSN: 1573-515X
    Keywords: grassland ; ground water level ; methane ; peat ; temperature ; wetland
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The area of wet grasslands on peat soil in the Netherlands is slowly increasing at the expense of drained, agriculturally used grasslands. This study aimed (i) to assess the contribution of wet grasslands on peat soil to methane (CH4) emissions, and (ii) to explain differences among sites and between years in order to improve our understanding of controlling factors. For these purposes, a field study was conducted in the period 1994–1996 in the nature preserve “Nieuwkoopse Plassen”, which is a former peat mining and agricultural area. Net CH4 emissions were measured weekly to monthly with vented closed flux chambers at three representative sites, and at ditches near these sites. Three-years average of CH4 emissions was 7.9 g CH4 m- 2 yr-1 for Drie Berken Zudde, 13.3 for Koole, and 20.4 for Brampjesgat. Ditches near the sites emitted 4.2–22.5 g CH4 m-2 yr-1. The time-course of CH4 emissions for all experimental sites and years was fit with a multiple linear regression model with ground water level and soil temperature as independent variables. Lowering or raising the ground water level by 5 cm could decrease or increase CH4 emissions by 30–50%. Therefore, ground water level management of these grasslands should be done with care.
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    Soil oxygen availability and biogeochemistry along rainfall and topographic gradients in upland wet tropical forest soils (1999)
    Springer
    Biogeochemistry 44 (1999), S. 301-328 
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    ISSN: 1573-515X
    Keywords: climate ; methane ; N2O ; Puerto Rico ; soil oxygen ; soil phosphorus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We measured soil oxygen concentrations at 10 and 35 cm depths and indices of biogeochemical cycling in upland forest soils along a rainfall and elevation gradient (3500–5000 mm y−1; 350–1050 masl) and along topographic gradients (ridge to valley, ∼150 m) in the Luquillo Experimental Forest, Puerto Rico. Along the rainfall gradient, soil O2 availability decreased significantly with increasing annual rainfall, and reached very low levels (〈3%) in individual chambers for up to 25 consecutive weeks over 82 weeks of study. Along localized topographic gradients, soil O2 concentrations were variable and decreased significantly from ridges to valleys. In the valleys, up to 35% of the observations at 10–35 cm depth were 〈3% soil O2. Cross correlation analyses showed that soil O2 concentrations were significantly positively correlated along the topographic gradient, and were sensitive to rainfall and hydrologic output. Soil O2 concentrations in valley soils were correlated with rainfall from the previous day, while ridge sites were correlated with cumulative rainfall inputs over 4 weeks. Soils at the wettest point along the rainfall gradient had very high soil methane concentrations (3–24%) indicating a strong influence of anaerobic processes. We measured net methane emission to the atmosphere at the wettest sites of the rainfall gradient, and in the valleys along topographic gradients. Other measures of biogeochemical function such as soil organic matter content and P availability were sensitive to chronic O2 depletion along the rainfall gradient, but less sensitive to the variable soil O2 environment exhibited at lower elevations along topographic gradients.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006034126698
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    Landscape patterns of CH4 fluxes in an alpine tundra ecosystem (1999)
    Springer
    Biogeochemistry 45 (1999), S. 243-264 
    Details
    ISSN: 1573-515X
    Keywords: alpine tundra ; methane ; trace gas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We measured CH4 fluxes from three major plant communities characteristic of alpine tundra in the Colorado Front Range. Plant communities in this ecosystem are determined by soil moisture regimes induced by winter snowpack distribution. Spatial patterns of CH4 flux during the snow-free season corresponded roughly with these plant communities. InCarex-dominated meadows, which receive the most moisture from snowmelt, net CH4 production occurred. However, CH4 production in oneCarex site (seasonal mean=+8.45 mg CH4 m−2 d−1) was significantly larger than in the otherCarex sites (seasonal means=−0.06 and +0.05 mg CH4 m−2 d−1). This high CH4 flux may have resulted from shallower snowpack during the winter. InAcomastylis meadows, which have an intermediate moisture regime, CH4 oxidation dominated (seasonal mean=−0.43 mg CH4 m−2 d−1). In the windsweptKobresia meadow plant community, which receive the least amount of moisture from snowmelt, only CH4 oxidation was observed (seasonal mean=−0.77 mg CH4 m−2 d−1). Methane fluxes correlated with a different set of environmental factors within each plant community. In theCarex plant community, CH4 emission was limited by soil temperature. In theAcomastylis meadows, CH4 oxidation rates correlated positively with soil temperature and negatively with soil moisture. In theKobresia community, CH4 oxidation was stimulated by precipitation. Thus, both snow-free season CH4 fluxes and the controls on those CH4 fluxes were related to the plant communities determined by winter snowpack.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00993002
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    The importance of floating peat to methane fluxes from flooded peatlands (1999)
    Springer
    Biogeochemistry 47 (1999), S. 187-202 
    Details
    ISSN: 1573-515X
    Keywords: boreal peatland ; floating peat ; methane ; reservoirs ; wetlands
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The effect of flooding on methane (CH4) fluxes was studied through the construction of an experimental reservoir in a boreal forest wetland at the Experimental Lakes Area in northwestern Ontario. Prior to flooding, the peatland surface was a small source of CH4 to the atmosphere (1.0 ± SD of 2.3 mg CH4 m−2 d−1). After flooding, CH4 fluxes from the submerged peat surface increased to 64±68 mg CH4 m−2 d−1. CH4 bubbles within the submerged peat caused about 1/3 of the peat to float. Fluxes from these floating peat islands were much higher (440±350 mg CH4 m−2 d−1) than from both the pre-flood (undisturbed) and the post-flood (submerged) peat surfaces. The high fluxes of CH4 from the floating peat surfaces may be explained by a number of factors known to affect the production and consumption of CH4 in peat. In floating peat, however, these factors are particularly enhanced and include decreased oxidation of CH4 due to the loss of aerobic habitat normally found above the water table of undisturbed peat and to increased peat temperatures. The extremely high fluxes associated with newly lifted peat may decrease as the islands age. However, CH4 flux rates from floating peat islands that were several years old still far exceeded those from undisturbed peat surfaces and from the water surface of a newly created reservoir.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006142026171
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  • 44
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    The importance of floating peat to methane fluxes from flooded peatlands (1999)
    Springer
    Biogeochemistry 47 (1999), S. 187-202 
    Details
    ISSN: 1573-515X
    Keywords: boreal peatland ; floating peat ; methane ; reservoirs ; wetlands
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The effect of flooding on methane (CH4) fluxes was studied through the construction of an experimental reservoir in a boreal forest wetland at the Experimental Lakes Area in northwestern Ontario. Prior to flooding, the peatland surface was a small source of CH4 to the atmosphere (1.0± SD of 2.3 mg CH4 m−2 d−1). After flooding, CH4 fluxes from the submerged peat surface increased to 64±68 mg CH4 m−2 d−1 CH4 bubbles within the submerged peat caused about 1/3 of the peat to float. Fluxes from these floating peat islands were much higher (440±350 mg CH4 m−2 d−2) than from both the pre-flood (undisturbed) and the post-flood (submerged) peat surfaces. The high fluxes of CH4 from the floating peat surfaces may be explained by a number of factors known to affect the production and consumption of CH4 in peat. In floating peat, however, these factors are particularly enhanced and include decreased oxidation of CH4 due to the loss of aerobic habitat normally found above the water table of undisturbed peat and to increased peat temperatures. The extremely high fluxes associated with newly lifted peat may decrease as the islands age. However, CH4 flux rates from floating peat islands that were several years old still far exceeded those from undisturbed peat surfaces and from the water surface of a newly created reservoir.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00994922
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  • 45
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    Landscape patterns of CH4 fluxes in an alpine tundra ecosystem (1999)
    Springer
    Biogeochemistry 45 (1999), S. 243-264 
    Details
    ISSN: 1573-515X
    Keywords: alpine tundra ; methane ; trace gas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We measured CH4 fluxes from three major plant communities characteristic of alpine tundra in the Colorado Front Range. Plant communities in this ecosystem are determined by soil moisture regimes induced by winter snowpack distribution. Spatial patterns of CH4 flux during the snow-free season corresponded roughly with these plant communities. In Carex-dominated meadows, which receive the most moisture from snowmelt, net CH4 production occurred. However, CH4 production in one Carex site (seasonal mean = +8.45 mg CH4 m-2 d-1) was significantly larger than in the other Carex sites (seasonal means = –0.06 and +0.05 mg CH4 m-2 d-1). This high CH4 flux may have resulted from shallower snowpack during the winter. In Acomastylis meadows, which have an intermediate moisture regime, CH4 oxidation dominated (seasonal mean = –0.43 mg CH4 m-2 d-1). In the windswept Kobresia meadow plant community, which receive the least amount of moisture from snowmelt, only CH4 oxidation was observed (seasonal mean = –0.77 mg CH4 m-2 d-1). Methane fluxes correlated with a different set of environmental factors within each plant community. In the Carex plant community, CH4 emission was limited by soil temperature. In the Acomastylis meadows, CH4 oxidation rates correlated positively with soil temperature and negatively with soil moisture. In the Kobresia community, CH4 oxidation was stimulated by precipitation. Thus, both snow-free season CH4 fluxes and the controls on those CH4 fluxes were related to the plant communities determined by winter snowpack.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006130911046
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  • 46
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    Ethylene and methane in the upper water column of the subtropical Atlantic (1999)
    Springer
    Biogeochemistry 44 (1999), S. 73-91 
    Details
    ISSN: 1573-515X
    Keywords: Atlantic ; ethylene ; methane ; sea-air exchange
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The vertical distributions of ethylene and methane in the upper water column of the subtropical Atlantic were measured along a transect from Madeira to the Caribbean and compared with temperature, salinity, oxygen, nutrients, chlorophyll-a, and dissolved organic carbon (DOC). Methane concentrations between 41.6 and 60.7 nL L-1 were found in the upper 20 m of the water column giving a calculated average flux of methane into the atmosphere of 0.82 μg m-2 h-1. Methane profiles reveal several distinct maxima in the upper 500 m of the water column and short-time variations which are presumably partly related to the vertical migration of zooplankton. Ethylene concentrations in near surface waters varied in the range of 1.8 to 8.2 nL L-1. Calculated flux rates for ethylene into the atmosphere were in the range of 0.41 to 1.35 μg m-2 h-1 with a mean of 0.83 μg m-2 h-1. Maximum concentrations of up to 39.2 nL L-1 were detected directly below the pycnocline in the western Atlantic. The vertical distributions of ethylene generally showed one maximum at the pycnocline (about 100 m depth) where elevated concentrations of chlorophyll-a, dissolved oxygen, and nutrients were also found; no ethylene was detected below 270 m depth. This suggests that ethylene release is mainly related to one, probably phytoplankton associated, source, while for methane, enhanced net production occurs at various depth horizons. For surface waters, a simple correlation between ethylene and chlorophyll-a or DOC concentrations could not be observed. No considerable diurnal variation was observed for the distribution and concentration of ethylene in the upper water column.
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    URL: http://dx.doi.org/10.1023/A:1006090917059
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  • 47
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    Winter CO2 CH4 and N2O fluxes on some natural and drained boreal peatlands (1999)
    Springer
    Biogeochemistry 44 (1999), S. 163-186 
    Details
    ISSN: 1573-515X
    Keywords: carbon dioxide ; gas gradients ; methane ; nitrous oxide ; peatland ; winter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract CO2 and CH4 fluxes during the winter were measured at natural and drained bog and fen sites in eastern Finland using both the closed chamber method and calculations of gas diffusion along a concentration gradient through the snowpack. The snow diffusion results were compared with those obtained by chamber, but the winter flux estimates were derived from chamber data only. CH4 emissions from a poor bog were lower than those from an oligotrophic fen, while both CO2 and CH4 fluxes were higher in the Carex rostrata-occupied marginal (lagg) area of the fen than in the slightly less fertile centre. Average estimated winter CO2-C losses from virgin and drained forested peatlands were 41 and 68 g CO2-C m- 2, respectively, accounting for 23 and 21% of the annual total CO2 release from the peat. The mean release of CH4-C was 1.0 g in natural bogs and 3.4 g m-2 in fens, giving rise to winter emissions averaging to 22% of the annual emission from the bogs and 10% of that from the fens. These wintertime carbon gas losses in Finnish natural peatlands were even greater than reported average long-term annual C accumulation values (less than 25 g C m-2). The narrow range of 10–30% of the proportion of winter CO2 and CH4 emissions from annual emissions found in Finnish peatlands suggest that a wider generalization in the boreal zone is possible. Drained forested bogs emitted 0.3 g CH4-C m-2 on the average, while the effectively drained fens consumed an average of 0.01 g CH4-C m- 2. Reason for the low CH4 efflux or net oxidation in drained peatlands probably lies in low substrate supply and thus low CH4 production in the anoxic deep peat layers. N2O release from a fertilized grassland site in November–May was 0.7 g N2O m-2, accounting for 38% of the total annual emission, while a forested bog released none and two efficiently drained forested fens 0.09 (28% of annual release) and 0.04 g N2O m- 2 (27%) during the winter, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006074606204
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  • 48
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    Winter CO2, CH4 and N2O fluxes on some natural and drained boreal peatlands (1999)
    Springer
    Biogeochemistry 44 (1999), S. 163-186 
    Details
    ISSN: 1573-515X
    Keywords: carbon dioxide ; gas gradients ; methane ; nitrous oxide ; peatland ; winter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract CO2 and CH4 fluxes during the winter were measured at natural and drained bog and fen sites in eastern Finland using both the closed chamber method and calculations of gas diffusion along a concentration gradient through the snowpack. The snow diffusion results were compared with those obtained by chamber, but the winter flux estimates were derived from chamber data only. CH4 emissions from a poor bog were lower than those from an oligotrophic fen, while both CO2 and CH4 fluxes were higher in theCarex rostrata- occupied marginal (lagg) area of the fen than in the slightly less fertile centre. Average estimated winter CO2-C losses from virgin and drained forested peatlands were 41 and 68 g CO2-C m−2, respectively, accounting for 23 and 21% of the annual total CO2 release from the peat. The mean release of CH4-C was 1.0 g in natural bogs and 3.4 g m−2 in fens, giving rise to winter emissions averaging to 22% of the annual emission from the bogs and 10% of that from the fens. These wintertime carbon gas losses in Finnish natural peatlands were even greater than reported average long-term annual C accumulation values (less than 25g C m−2). The narrow range of 10–30% of the proportion of winter CO2 and CH4 emissions from annual emissions found in Finnish peatlands suggest that a wider generalization in the boreal zone is possible. Drained forested bogs emitted 0.3 g CH4-C m−2 on the average, while the effectively drained fens consumed an average of 0.01 g CH4-C m−2. Reason for the low CH4. efflux or net oxidation in drained peatlands probably lies in low substrate supply and thus low CH4 production in the anoxic deep peat layers. N2O release from a fertilized grassland site in November–May was 0.7 g N2O m−2, accounting for 38% of the total annual emission, while a forested bog released none and two efficiently drained forested fens 0.09 (28% of annual release) and 0.04 g N2O m−2 (27%) during the winter, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00992977
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  • 49
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    Methane emissions from wet grasslands on peat soil in a nature preserve (1999)
    Springer
    Biogeochemistry 44 (1999), S. 205-220 
    Details
    ISSN: 1573-515X
    Keywords: grassland ; ground water level ; methane ; peat ; temperature ; wetland
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The area of wet grasslands on peat soil in the Netherlands is slowly increasing at the expense of drained, agriculturally used grasslands. This study aimed (i) to assess the contribution of wet grasslands on peat soil to methane (CH4) emissions, and (ii) to explain differences among sites and between years in order to improve our understanding of controlling factors. For these purposes, a field study was conducted in the period 1994–1996 in the nature preserve “Nieuwkoopse Plassen”, which is a former peat mining and agricultural area. Net CH4 emissions were measured weekly to monthly with vented closed flux chambers at three representative sites, and at ditches near these sites. Three-years average of CH4 emissions was 7.9 g CH4 m−2 yr−1 for Drie Berken Zudde, 13.3 for Koole, and 20.4 for Brampjesgat. Ditches near the sites emitted 4.2–22.5 g CH4 m−2 yr−1. The time-course of CH4 emissions for all experimental sites and years was fit with a multiple linear regression model with ground water level and soil temperature as independent variables. Lowering or raising the ground water level by 5 cm could decrease or increase CH4 emissions by 30–50%. Therefore, ground water level management of these grasslands should be done with care.
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    URL: http://dx.doi.org/10.1007/BF00992979
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  • 50
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    Determinants of spatial variability of methane emissions from wet grasslands on peat soil (1999)
    Springer
    Biogeochemistry 44 (1999), S. 221-237 
    Details
    ISSN: 1573-515X
    Keywords: grassland ; methane ; peat ; spatial variability ; wetland
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Methane (CH4) emissions from soils, representing the consequence of CH4 production, CH4 consumption and CH4 transport, are poorly characterised and show a large spatial variability. This study aimed to assess the determinants of field-scale spatial variability of CH4 emissions from wet grasslands on peat soil. Mean CH4 emission rates of a three-year experiment at 18 plots distributed over three sites in the nature preserve “Nieuwkoopse Plassen” on peat soil in the Netherlands were related to CH4 production and CH4 consumption capacities of soil layers, and to soil and vegetation characteristics. Spatial variability of CH4 emissions and possible determining factors was high. Annual CH4 emissions ranged from 3 to 37 g CH4 m−2 yr−1. Coefficients of variation (CV) of CH4 emissions were on average 37% among sites and 83% within sites. Most important determinants of spatial variability were CH4 production capacity (average: 211 ng CH4 g−1 dry soil h−1; CV: 131%) and aboveground biomass of sedges (Carex spp.) (average: 0.45 g dm−2; CV: 127%) (P〈0.01). Sedges may affect CH4 emissions by stimulating CH4 transport from anaerobic layers to the surface via their vascular system and/or by serving as substrate for methanogens. For extrapolation of CH4 emissions to larger areas, best results will be obtained by using factors that are easy to determine, like vegetation.
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    URL: http://dx.doi.org/10.1007/BF00992980
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  • 51
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    Soil oxygen availability and biogeochemistry along rainfall and topographic gradients in upland wet tropical forest soils (1999)
    Springer
    Biogeochemistry 44 (1999), S. 301-328 
    Details
    ISSN: 1573-515X
    Keywords: climate ; methane ; N2O ; Puerto Rico ; soil oxygen ; soil phosphorus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We measured soil oxygen concentrations at 10 and 35 cm depths and indices of biogeochemical cycling in upland forest soils along a rainfall and elevation gradient (3500–5000 mm y−1; 350–1050 masl) and along topographic gradients (ridge to valley, ∼150 m) in the Luquillo Experimental Forest, Puerto Rico. Along the rainfall gradient, soil O2 availability decreased significantly with increasing annual rainfall, and reached very low levels (〈3%) in individual chambers for up to 25 consecutive weeks over 82 weeks of study. Along localized topographic gradients, soil O2 concentrations were variable and decreased significantly from ridges to valleys. In the valleys, up to 35% of the observations at 10–35 cm depth were 〈3% soil O2. Cross correlation analyses showed that soil O2 concentrations were significantly positively correlated along the topographic gradient, and were sensitive to rainfall and hydrologic output. Soil O2 concentrations in valley soils were correlated with rainfall from the previous day, while ridge sites were correlated with cumulative rainfall inputs over 4 weeks. Soils at the wettest point along the rainfall gradient had very high soil methane concentrations (3–24%) indicating a strong influence of anaerobic processes. We measured net methane emission to the atmosphere at the wettest sites of the rainfall gradient, and in the valleys along topographic gradients. Other measures of biogeochemical function such as soil organic matter content and P availability were sensitive to chronic O2 depletion along the rainfall gradient, but less sensitive to the variable soil O2 environment exhibited at lower elevations along topographic gradients.
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    URL: http://dx.doi.org/10.1007/BF00996995
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    Microwave effect on partial oxidation of methane to syngas (1999)
    Springer
    Reaction kinetics and catalysis letters 66 (1999), S. 381-386 
    Details
    ISSN: 1588-2837
    Keywords: Microwave ; methane ; partial oxidation ; syngas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In this paper the results of the partial oxidation of methane over Ni-based and Co-based catalysts activated by two different heating modes (conventional and microwaves) are reported. Compared with a conventional heating mode, the temperature of the catalytic bed is much lower and there is a higher selectivity of CO and H2 with microwave irradiation.
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    URL: http://dx.doi.org/10.1007/BF02475816
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    Effect of metal oxides on the reforming of methane with carbon dioxide (1999)
    Springer
    Reaction kinetics and catalysis letters 68 (1999), S. 183-190 
    Details
    ISSN: 1588-2837
    Keywords: Reforming ; methane ; carbon dioxide ; catalyst ; metal oxide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The effect of basic and rare earth metal oxides on the stability of nickel-based catalysts for the CO2 reforming of CH4 has been studied. The addition of metal oxides increased the stability of Ni-based catalysts and reversed the values of the reaction orders with respect to both CH4 and CO2. In the presence of metal oxides, the values of the reaction orders with respect to CO2 partial pressure followed the same trend of catalyst stability.
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    URL: http://dx.doi.org/10.1007/BF02475500
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  • 54
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    Mechanism of the partial oxidation of methane to synthesis gas over Pd (1998)
    Springer
    Catalysis letters 50 (1998), S. 59-67 
    Details
    ISSN: 1572-879X
    Keywords: partial oxidation ; synthesis gas ; methane ; palladium ; carbon filaments
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The partial oxidation of methane to synthesis gas has been studied in an isothermal continuous flow reactor operated with the phases in plug flow, using a silica-supported palladium catalyst. The reaction mechanism involves the sequential combustion and reforming of methane. The catalyst bed is not uniform in terms of the composition of the palladium phase. The implications for investigations using a pulse apparatus are discussed. Finally, large palladium crystallites readily grow carbon filaments.
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    URL: http://dx.doi.org/10.1023/A:1019090213003
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    Pd–Pt bimetallic catalyst supported on SAPO‐5 for catalytic combustion of diluted methane in the presence of water vapor (1998)
    Springer
    Catalysis letters 53 (1998), S. 167-169 
    Details
    ISSN: 1572-879X
    Keywords: methane ; combustion ; water vapor ; ion‐exchanged SAPO ; Pd–Pt bimetal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The examination of the combustion of a trace amount of methane over Pd‐ion‐exchanged silicoaluminophosphate‐5 (Pd‐SAPO‐5) at low temperature in the presence of water vapor reveals that water vapor strongly depresses methane combustion and causes a significant decrease in catalytic activity with time. The newly prepared bimetallic catalyst Pd–Pt‐SAPO‐5, on the other hand, shows higher performance for methane combustion under similar conditions.
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    URL: http://dx.doi.org/10.1023/A:1019082611978
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    Effect of support on the conversion of methane to synthesis gas over supported iridium catalysts (1998)
    Springer
    Catalysis letters 51 (1998), S. 163-167 
    Details
    ISSN: 1572-879X
    Keywords: methane ; partial oxidation ; carbon dioxide ; reforming ; iridium ; titania ; synthesis gas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A partial oxidation of methane was carried out using iridium catalysts supported on several metal oxides. The productivity of the synthesis gas from methane was strongly affected by the choice of support oxides for the catalysts. The synthesis gas production proceeded basically via a two-step reaction consisting of methane combustion to give H2O and CO2, followed by the reforming of methane from CO2 and steam. Although the combustion and the reforming of methane from steam did not depend upon the catalyst support, a large variation in the catalytic activity for the reforming of methane from CO2 was observed over Ir catalysts with different supports. The support activity order in the reforming of methane from CO2 with iridium catalysts was as follows: TiO2≧ZrO2≧Y2O3〉La2O3〉MgO≧Al2O3〉SiO2. The same order was observed in the synthesis gas production from the partial oxidation of methane.
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    URL: http://dx.doi.org/10.1023/A:1019065824331
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    Cobalt catalysts in selective catalytic reduction of NO by methane (1998)
    Springer
    Catalysis letters 51 (1998), S. 191-194 
    Details
    ISSN: 1572-879X
    Keywords: montmorillonite ; selective catalytic reduction of NO ; methane ; water ; role of O2 ; oxide-oxide interaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Impregnated cobalt-containing catalysts are studied in the selective catalytic reduction of NO by methane. The active component of all the impregnated cobalt-containing catalysts is Co3O4. The role of O2 seems to maintain the surface stoichiometry of Co3O4. The main reason of decrease of catalytic activity of samples based on MgO, SiO2, Al2O3 in selective catalytic reduction of NO is due to oxide-oxide interaction promoted by water. Catalysts based on montmorillonite (HMM) are stable in the presence of water. All the carriers can be placed by the capability for oxide–oxide interaction in the following order: SiO2 ≫ MgO 〉 Al2O3 ≫ HMM.
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    URL: http://dx.doi.org/10.1023/A:1019082327966
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    Methane conversion to ethane in the presence of iron‐ and manganese‐promoted sulfated zirconia (1998)
    Springer
    Catalysis letters 53 (1998), S. 1-2 
    Details
    ISSN: 1572-879X
    Keywords: methane ; sulfated zirconia ; promoted sulfated zirconia ; ethane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Sulfated zirconia promoted with 1.0 wt% Fe and 0.5 wt% Mn converts methane into ethane with traces of ethylene and acetylene. The initial reaction rate at 723 K and a methane partial pressure of 20 kPa was found to be about 10-9 mol(CH 4) (g s)-1, and deactivation was rapid, with the reaction rate declining to half the maximum rate within an hour.
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    URL: http://dx.doi.org/10.1023/A:1019029100166
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    Partial oxidation of methane to syngas using NiO‐supported catalysts (1998)
    Springer
    Catalysis letters 51 (1998), S. 177-181 
    Details
    ISSN: 1572-879X
    Keywords: methane ; nickel oxide ; synthesis gas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Claims for the partial oxidation of methane to CO and H2 have been clouded by the possibility of the indirect reaction sequence occurring at hot spots in the catalyst bed. In this report, we claim that the direct reaction occurs on NiO/silica at 500°C with methane conversions as high as 80% and selectivities for H2 of 80% and CO of 70%. Arguments are presented to show that the amount of diluent gas employed prevents formation of local hot spots with temperatures high enough for the indirect reaction to occur. Consequently, this study constitutes one of the most convincing reports for the conversion of CH4 to syngas by the partial oxidation of methane. The catalyst deactivates in 10 h. Surface studies show coke formation and aggregation of NiO contribute to the loss of activity.
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    Nonoxidative dehydrogenation and aromatization of methane over W/HZSM‐5‐based catalysts (1998)
    Springer
    Catalysis letters 53 (1998), S. 119-124 
    Details
    ISSN: 1572-879X
    Keywords: methane ; dehydro‐aromatization ; W/HZSM‐5 ; W–H2SO4/HZSM‐5 ; W–Zn (or La)–H2SO4/HZSM‐5 ; polytungstates ; promoting effect of Zn or La
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Highly active and heat‐resisting W/HZSM‐5‐based catalysts for nonoxidative dehydro‐aromatization of methane (DHAM) have been developed and studied. It was found from the experiments that the W−H2SO4/HZSM−5 catalyst prepared from a H2SO4‐acidified solution of ammonium tungstate (with a pH value at 2–3) displayed rather high DHAM activity at 973–1023 K, whereas the W/HZSM‐5 catalyst prepared from an alkaline or neutral solution of (NH4)2WO4 showed very little DHAM activity at the same temperatures. Laser Raman spectra provided evidence for existence of (WO6)n- groups constructing polytungstate ions in the acidified solution of ammonium tungstate. The H2‐TPR results showed that the reduction of precursor of the 3% W–H2SO4/HZSM‐5 catalyst may occur at temperatures below 900 K, producing W species with mixed valence states, W5+ and W4+, whereas the reduction of the 3% W/HZSM‐5 occurred mainly at temperatures above 1023 K, producing only one type of dominant W species, W5+. The results seem to imply that the observed high DHAM activity on the W–H2SO4/HZSM‐5 catalyst was closely correlated with (WO6)n- groups with octahedral coordination as the precursor of catalytically active species. Incorporation of Zn (or La) into the W–H2SO4/HZSM‐5 catalyst has been found to pronouncedly improve the activity and stability of the catalyst for DHAM reaction. Over a 2.5% W–1.5% Zn–H2SO4/HZSM‐5 catalyst and under reaction conditions of 1123 K, 0.1 MPa, and GHSV=1500 ml/(h g−cat.), methane conversion (XCH4) reached 23% with the selectivity to benzene at ∼96% and an amount of coke for 3 h of operation at 0.02% of the catalyst weight used.
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    Synthesis, structure and catalytic properties of Fe-substituted barium hexaaluminates (1998)
    Springer
    Catalysis letters 54 (1998), S. 141-148 
    Details
    ISSN: 1572-879X
    Keywords: catalytic combustion ; methane ; iron ; barium hexaaluminates ; aging ; Mössbauer spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A sol–gel method using Ba and Al isopropylates and iron nitrate has been used to synthesise barium hexaaluminate partially substituted with iron. After calcination under oxygen at 1200°C the β-alumina structure was obtained. Formation of the mixed BaFexAl12-xO19 phase occurred for x=1–4. XRD measurements showed a good crystallinity of the structure and expansion of unit cell parameters due to the presence of larger Fe3+ ions substituting Al3+ ones in octahedral sites only. Mössbauer spectroscopy revealed that Fe3+ ions are present in four different octahedral sites slightly distorted. Catalytic activity in methane combustion showed that an optimum was obtained for solid containing 2 Fe ions per unit cell: the increase of the amount of introduced iron was counterbalanced by the decrease of specific surface area. Intrinsic activities have been calculated for the four solids in both the fresh and aged states. It is observed that increasing iron content increases relative activities in the same ratio as the populations of iron located in two sites as deduced from Mössbauer spectroscopy. It is then tentatively assumed that activity is attributed to octahedrally coordinated Fe3+ ions in some specific sites.
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    Remarkable enhancing effect of carbon dioxide on the conversion of methane to C2 hydrocarbons using praseodymium oxide (1998)
    Springer
    Catalysis letters 56 (1998), S. 203-206 
    Details
    ISSN: 1572-879X
    Keywords: methane ; carbon dioxide ; oxygen vacancies ; praseodymium oxide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The presence of carbon dioxide remarkably enhanced the conversion of methane to ethane over praseodymium oxide in the absence of gaseous oxygen at 500–650°C. CO was simultaneously formed from CO2 accompanying the conversion of methane. The oxygen vacancies in praseodymium oxide were suggested to play key roles in this low-temperature reaction.
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    URL: http://dx.doi.org/10.1023/A:1019073415980
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    Partial Oxidation of Methane to Methanol with Oxygen or Air in a Nonequilibrium Discharge Plasma (1998)
    Springer
    Plasma chemistry and plasma processing 18 (1998), S. 375-393 
    Details
    ISSN: 1572-8986
    Keywords: Greenhouse gases ; methane ; methanol synthesis ; dielectric-barrier discharge (DBD) ; methane oxidation ; plasma chemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract The partial oxidation of methane to methanol with oxygen or air was investigated experimentally and theoretically in a dielectric-barrier discharge (DBD). The predominant parameters of specific electric energy, oxygen content, flow rate, temperature, and gas pressure were determined in CH 4 /O 2 and CH 4 /air mixtures. Optimum selectivities toward methanol formation were found at an oxygen concentration of about 15% in both feed gas mixtures. Low specific energy favors the selectivity toward methanol and suppresses the formation of carbon oxides. The experiments indicate that high methanol selectivities can be obtained at high methane conversion. The highest methanol yield of 3% and the highest methanol selectivity of about 30% were achieved in CH 4 /O 2 mixtures. In CH 4 /air mixtures, as high as 2% methanol yield was also obtained. In addition, other useful products, like ethylene, ethane, propane, and ethanol, were detected. Experiment and numerical simulations show that the formation of H 2 O and CO has a strong negative influence on methanol formation.
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    The Multiple Sources and Patterns of Methane inNorth Sea Waters (1998)
    Springer
    Aquatic geochemistry 4 (1998), S. 403-427 
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    ISSN: 1573-1421
    Keywords: methane ; trace gases ; North Sea ; air-sea exchange
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The methane concentration in the atmosphere andsurface water was surveyed along 58° N acrossthe North Sea. In addition, the vertical methanedistribution in the water column was determined at sixstations along the transect. The methane contents ofthe surface water as well as in the water column wereextremely inhomogeneous. Input by freshwater fromriver discharge and injection of methane from thesediment were both observed. The survey continued fromthe western side of the North Sea to the Elbe Riverestuary. The Elbe River appears to have low methaneconcentrations compared to other European rivers, itsaverage input into the North Sea is estimated to be70 nmol s-1 of methane. Near 58° N,1°40' E, an abandoned drill site releases about 25 % ofthe North Sea's emission of methane to the atmosphere.The advective methane transport induced by watercirculation was assessed for May 16, 1994, using a 3-DNorth Sea circulation model. For the period of thissurvey, the North Sea's source strength foratmospheric methane is estimated using in situwind velocities. In comparison to the advectivetransport by the water circulation, the gas flux tothe atmosphere appears to be the dominant sink ofNorth Sea methane. This flux is estimated to bebetween 1500 · 106 mol a-1 and 3100 ·106mol a-1, depending on the relationbetween wind speed and gas transfer velocity.
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    Hysteresis in the temperature response of carbon dioxide and methane production in peat soils (1998)
    Springer
    Biogeochemistry 43 (1998), S. 253-272 
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    ISSN: 1573-515X
    Keywords: carbon dioxide ; hysteresis ; methane ; peat ; temperature ; wetlands
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The ability to predict the effects of climate change on trace gas fluxes requires a knowledge of microbial temperature responses. However, the response of a microbial community to temperature in a given substrate may be complicated by its thermal history. To examine the effect of sequentially changing temperature on methane and carbon dioxide production in different peat types, we incubated anaerobic peat samples from 3 types of northern peatlands, a bog, a sedge fen and a cedar swamp, in both rising and falling temperature regimes. Graphic and statistical comparisons of the different temperature regimes suggest hysteresis in microbial response to temperature, although the absolute rates at any given temperature often did not differ. Where regressions for temperature response (Arrhenius plots) were significant, they generally differed between temperature regimes. The greatest differences among treatments occurred during the first half of the 40-d incubation. Increases in carbon dioxide production were similar across all peat types, but methanogenesis varied widely: methane production was uniformly low in the bog peat but increased sharply with temperature in the other two peat types. The complicating effect of history or chronology on substrate responses to environmental stimuli may restrain our ability to model the responses of complex systems to changing conditions.
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    Characterization of microbial NO production, N2O production and CH4 oxidation initiated by aeration of anoxic rice field soil (1998)
    Springer
    Biogeochemistry 40 (1998), S. 17-36 
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    ISSN: 1573-515X
    Keywords: drainage ; denitrification ; methane ; nitric oxide ; nitrous oxide ; nitrification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Intermittent drainage of rice fields isdiscussed as an option to mitigate emission ofCH4, an important greenhouse gas. HoweverN2O, a potentially more effective greenhouse gas,may be emitted during the aeration phase. Therefore,the metabolism of NO, N2O, NH $$_4^ + $$ ,NO $$_2^ - $$ and NO $$_3^ - $$ and the kinetics ofCH4 oxidation were measured after aeration ofmethanogenic rice field soil. Before aeration, thesoil contained NH $$_4^ + $$ in relatively highconcentrations (about 4 mM), while NO $$_2^ - $$ andNO $$_3^ - $$ were almost undetectable. Immediatelyafter aeration both NO and N2O were produced withrates of about 15 pmol h-1 gdw-1 and 5 pmolh-1 gdw-1, respectively. Simultaneously,NH $$_4^ + $$ decreased while NO $$_2^ - $$ accumulated. Later on, NO $$_2^ - $$ was depletedwhile NO $$_3^ - $$ concentrations increased.Characteristic phases of nitrogen turnover wereassociated with the activities of ammonium oxidizers,nitrite oxidizers and denitrifiers. Oxidation ofNH $$_4^ + $$ and production of NO and N2O wereinhibited by 10 Pa acetylene demonstrating thatnitrification was obligatory for the initiation ofnitrogen turnover and production of NO and N2O.Ammonium oxidation was not limited by the availableNH $$_4^ + $$ and thus, concomittant production of NOand N2O was not stimulated by addition ofNH $$_4^ + $$ . However, addition of NO $$_3^ - $$ stimulated production of NO and N2O in bothanoxic and aerated rice soil slurries. In this case,10 Pa acetylene did not inhibit the production of NOand N2O demonstrating that it was due todenitrification which was obviously limited by theavailability of NO $$_3^ - $$ . In the aerated soilslurries CH4 was only oxidized if present atelevated concentrations 〉50 ppmv CH4). Atatmospheric CH4 concentrations (∼1.7 ppmv)CH4 was not consumed, but was even slightly produced.CH4 oxidation activity increased afterpreincubation at 20% CH4, and then CH4was also oxidized at atmospheric concentrations. CH4oxidation kinetics exhibited sigmoid characteristicsat low CH4 concentrations presumably because ofinhibition of CH4 oxidation by NH $$_4^ + $$ .
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    Trace Gas Measurements Between Moscow and Vladivostok Using the Trans-Siberian Railroad (1998)
    Springer
    Journal of atmospheric chemistry 29 (1998), S. 179-194 
    Details
    ISSN: 1573-0662
    Keywords: tropospheric chemistry ; ozone ; Russia ; trans-Siberian railroad ; Siberia ; carbon monoxide ; methane ; nitrogen oxides ; trace gases ; atmospheric composition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Using a laboratory wagon traveling along the Trans-Siberian railroad, O3, NO, NO2, CO, CH4, SF6 and black carbon aerosol have been measured during the summer of 1996. The expedition from Niznij Novgorod (500 km east of Moscow) to Vladivostok (and back to Moscow) has shown the great potential of the train method; here the first results are presented and discussed. A wealth of boundary layer air data was obtained during the over 18000 km travel without serious contamination problems from the electric train itself. The diurnal O3 cycle peaked generally below 50 nmole/mole, showed the effects of changes in J(NO2), and often dropped to a few nmole/mole at night time during inversions. Over the vast Siberian lowlands situated between the Ural mountains and the river Yenisey, CH4 levels were consistently elevated at around 1.95 µmole/mole, which we mainly attribute to wetland emissions. Over eastern Siberia, however, CH4 levels were generally lower at 1.85 µmole/mole. In contrast, over the west Siberian lowlands, CO levels were relatively low, often reaching values of only 110 nmole/mole, whereas over eastern Siberia CO levels were higher. Very high CO levels were detected over a 2000 km section east of Chita, along the river Amur, which represented an enormous polluted air mass. 14C analysis performed on several CO samples confirms that the origin was biomass burning. SF6, which was measured as a general conserved tracer, showed an eastward attenuation from 4.0 to 3.9 pmole/mole, with peaks in a number of places due to local Russian emissions.
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    Response of tundra CH4 and CO2 flux tomanipulation of temperature and vegetation (1998)
    Springer
    Biogeochemistry 41 (1998), S. 215-235 
    Details
    ISSN: 1573-515X
    Keywords: arctic ; carbon dioxide ; climate change ; methane ; plant transport ; species composition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We conducted plant species removals, air temperaturemanipulations, and vegetation and soil transplants inAlaskan wet-meadow and tussock tundra communities todetermine the relative importance of vegetation typeand environmental variables in controlling ecosystemmethane (CH4) and carbon dioxide (CO2) flux. Plastic greenhouses placed over wet-meadow tundraincreased air temperature, soil temperature, and soilmoisture, but did not affect CH4 or CO2 flux(measured in the dark). By contrast, removal ofsedges in the wet meadow significantly decreased fluxof CH4, while moss removal tended to increaseCH4 emissions. At 15 cm depth, pore-waterCH4 concentrations were higher in sedge-removalthan in control plots, suggesting that sedgescontribute to CH4 emissions by transportingCH4 from anaerobic soil to the atmosphere, ratherthan by promoting methanogenesis. Inreciprocal-ecosystem transplants between thewet-meadow and tussock tundra communities, CH4and CO2 emissions were higher overall in thewet-meadow site, but were unrelated to transplantorigin. Methane flux was correlated with localvariation in soil temperature, thaw depth, andwater-table depth, but the relative importance ofthese factors varied through the season. Our resultssuggest that future changes in CH4 and CO2flux in response to climatic change will be morestrongly mediated by large-scale changes in vegetationand soil parameters than by direct temperature effects.
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    Influence of drainage basin topography and elevation on carbon dioxide and methane supersaturation of stream water (1998)
    Springer
    Biogeochemistry 40 (1998), S. 57-72 
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    ISSN: 1573-515X
    Keywords: carbon dioxide ; eastern Tennessee ; ecosystem metabolism ; methane ; streams ; Smoky Mountains
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The partial pressures of CO2 (pCO2) andCH4 (pCH4) in streams are not only governed byinstream processes, but also by transformations occurring in soil andgroundwater ecosystems. As such, stream water pCO2 andpCH4 can provide a tool to assess ecosystem respiration andanaerobic metabolism throughout drainage basins. We conducted three surveyssampling the gas content of streams in eastern Tennessee and western NorthCarolina to assess factors regulating ecosystem metabolism in catchmentswith contrasting geomorphologies, elevations and soil organic matterstorage. In our first survey, the influence of drainage basin geomorphologyon ecosystem respiration was examined by sampling streams drainingcatchments underlain by either shale or dolomite. Geomorphology isinfluenced by geology with shale catchments having shallower soils, broader,unconstrained valley floors compared with dolomite catchments.pCO2 varied little between catchment types but increased froman average of 3340 ppmv in spring to 9927 ppmv in summer or 9.3 and 28 timesatmospheric equilibrium (pCO2(equilib)), respectively. Incontrast, pCH4 was over twice as high in streams drainingshale catchments (306 ppmv; pCH4(equilib) = 116) compared withmore steeply incised dolomite basins (130 ppmv; pCH4(equilib)= 51). Using the ratio of pCH4:pCO2 as an indexof anaerobic metabolism, shale catchments had nearly twice as muchanaerobiosis (pCH4:pCO2 = 0.046) than dolomitedrainages (pCH4:pCO2 = 0.024). In our secondsurvey, streams were sampled along an elevational gradient (525 to 1700 m)in the Great Smoky Mountains National Park, USA where soil organic matterstorage increases with elevation. pCO2 did not vary betweenstreams but increased from 5340 ppmv (pCO2(equilib) = 15) to8565 ppmv (pCO2(equilib) = 24) from spring to summer,respectively. During spring pCH4 was low and constant acrossstreams, but during summer increased with elevation ranging from 17 to 2068ppmv (pCH4(equilib) = 10 to 1216). The contribution ofanaerobiosis to total respiration was constant during spring(pCH4:pCO2 = 0.017) but during summer increasedwith elevation from 0.002 at 524 m to 0.289 at 1286 m. In our last survey,we examined how pCO2 and pCH4 changed withcatchment size along two rivers (ca. 60 km stretches in both riverscorresponding to increases in basin size from 1.7–477km2 and 2.5–275 km2). pCO2and pCH4 showed opposite trends, with pCO2decreasing ca. 50% along the rivers, whereas pCH4roughly doubled in concentration downstream. These opposing shifts resultedin a nearly five-fold increase of pCH4:pCO2along the rivers from a low of 0.012 in headwaters to a high of 0.266 65-kmdownstream. pCO2 likely declines moving downstream asgroundwater influences on stream chemistry decreases, whereaspCH4 may increase as the prevalence of anoxia in riversexpands due to finer-grained sediments and reduced hydrologic exchange withoxygenated surface water.
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    Activation of CH4, CO2 and their reactions over Co catalyst studied using a pulsed-flow micro-reactor (1998)
    Springer
    Reaction kinetics and catalysis letters 64 (1998), S. 365-371 
    Details
    ISSN: 1588-2837
    Keywords: Activation ; methane ; carbon dioxide ; pulse reaction ; Co/Al2O3 catalyst
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Pulse reaction showed that Co/Al2O3 catalyst was active for the high-temperature decomposition of CH4 and CO2. CH4 mainly was completely decomposed to give surface carbon, which could be inactivated quickly in the absence of enough O(ad) (arising from dissociation of CO2). CO2 was dissociatively adsorbed on Co(0) sites to give CO(ad) and O(ad), which was a slow step. Further decomposition of CO(ad) happened in the case of CO2 decomposition.
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    An analytical method of micropore filling of a supercritical gas (1997)
    Springer
    Adsorption 3 (1997), S. 197-208 
    Details
    ISSN: 1572-8757
    Keywords: micropore filling ; supercritical gas ; carbon micropore ; nitrogen monooxide ; methane ; molecular assembly
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The supercritical gas adsorbed in the micropore having a strong molecular field was presumed to transform into the quasi-vapor to be filled in the micropore (quasi-vaporization adsorption mechanism). The Dubinin-Radushkevitch (DR) equation for micropore filling of vapor was extended to the quasi-vaporized supercritical gas using the quasi-saturated vapor pressureP 0 q and the inherent micropore volumeW L . The reason why the concepts ofP 0q andW L were introduced was explained with the molecule-pore interaction potential theory which is based on the Lennard-Jones interaction. The extended DR equation was named the supercritical DR equation. TheW L was evaluated by the Langmuir plot of the adsorption isotherm for a supercritical gas and both ofP 0q andW L provided the single reduced adsorption isotherms of supercritical NO, N2, and CH4 on activated carbon fibers and high surface area carbons were analyzed by the supercritical DR plots. The wide applicability of the reduced adsorption isotherm to these adsorption data was explicity shown. The two phase model of the organized and confined fluids was proposed in order to improve the quasi-vaporization adsorption mechanism.
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    Calculation of the metal-carbon bond strength of surface carbon deposited on solid oxide fuel cell nickel/zirconia fuel reforming anodes (1997)
    Springer
    Catalysis letters 49 (1997), S. 189-192 
    Details
    ISSN: 1572-879X
    Keywords: solid oxide fuel cells ; fuel reforming anodes ; steam reforming ; methane ; nickel ; yttria-stabilised zirconia ; temperature-programmed oxidation ; adsorption ; surface carbon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The activation energy for the removal of surface carbon formed by methane decomposition following high-temperature reforming, from a nickel/zirconia solid oxide fuel cell (SOFC) anode has been calculated using two methods based on temperature-programmed oxidation. It is found that there is a fairly good agreement between the two methods. In addition, it was observed that the addition of small quantities of lithium to the anode resulted in a significant lowering of the activation energy for surface carbon removal by about 50 kJ mol-1.
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    Methane flux from Missippi River deltaic plain wetlands (1997)
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    Biogeochemistry 37 (1997), S. 227-236 
    Details
    ISSN: 1573-515X
    Keywords: Louisiana USA ; wetlands ; methane ; methanogensis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Methane emissions from three wetland habitats in the MississippiRiver deltaic plain were measured over a three year period. Fluxdata collected indicate that each habitat was a net source of methane to the atmosphere throughout the year. Average emissionfrom a Taxodium distichum / Nyssa aquatica (bald cypress / watertupelo) swamp forest was 146 ± 199 mgCH4 m-2d-1 whileemissions from a Sagittaria lancifolia (bulltongue) freshwatermarsh averaged 251 ± 188 mg CH4m-2d-1. Methane flux from a Spartina patens / Sagittaria lancifolia intermediate marsh was significantlyhigher, 912 ± 923 mg CH4m-2d-1. Seasonal variation wassignificant with emissions being higher in the late summer andearly fall. Significant diurnal emissions were observed fromthe Sagittaria lancifolia marsh site. Soil temperature (5 and 10 cm depths) was found to be significantly correlated with methaneemission from the three sites.
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    Enhanced CH4 emission from a wetland soil exposed to Elevated CO2 (1997)
    Springer
    Biogeochemistry 37 (1997), S. 77-88 
    Details
    ISSN: 1573-515X
    Keywords: climate change ; elevated carbon dioxide ; hydrology ; methane ; transpiration ; wetlands
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Methane emissions from wetland soils are generally a positive function ofplant size and primary productivity, and may be expected to increase dueto enhanced rates of plant growth in a future atmosphere of elevatedCO2. We performed two experiments with Orontium aquaticum, acommon emergent aquatic macrophyte in temperate and sub-tropical wetlands, todetermine if enhanced rates of photosynthesis in elevated CO2atmospheres would increase CH4 emissions from wetland soils.O. aquaticum was grown from seed in soil cores under ambient and elevated(ca. 2-times ambient) concentrations of CO2 in an initialglasshouse study lasting 3 months and then a growth chamber study lasting 6months. Photosynthetic rates were 54 to 71% higher underelevated CO2 than ambient CO2, but plantbiomass was not significantly different at the end of the experiment. Ineach case, CH4 emissions were higher under elevated thanambient CO2 levels after 2 to 4 months of treatment, suggestinga close coupling between photosynthesis and methanogenesis in our plant-soilsystem. Methane emissions in the growth chamber study increased by 136%. We observed a significant decrease in transpirationrates under elevated CO2 in the growth chamber study, andspeculate that elevated CO2 may also stimulate CH4 emissions by increasing the extent and duration offlooding in some wetland ecosystems. Elevated CO2 maydramatically increase CH4 emissions from wetlands, a sourcethat currently accounts for 40% of global emissions.
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    Investigation of the methyl fluoride technique for determining rhizospheric methane oxidation (1997)
    Springer
    Biogeochemistry 36 (1997), S. 153-172 
    Details
    ISSN: 1573-515X
    Keywords: aquatic marcrophytes ; methane ; methane oxidation ; methyl fluoride ; plant/microbial ; interactions ; rhizosphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Methane oxidation rates in the rhizosphere of Pontederia cordata,Sagittaria lancifolia, and Typha latifolia were quantified in fieldstudies using the methyl fluoride inhibition technique. An averageoxidation of 22.9 ± 17.7% (sd,n = 44) was found for all field experiments (oxidation is expressedas a % of total potential emission in the presumedabsence of oxidation). Greenhouse experiments using the same techniquegave an average rhizospheric oxidation of 64.9 ±17.0% (sd, n = 44). Comparison of a subset ofgreenhouse plants with the methyl fluoride (MF) and a light oxic/darkanoxic (LO/DA) technique for suppressing CH4 oxidationyielded similar percentages (57.7 ±15.0% for MF and 58.5 ±13.9% for LO/DA, n = 11). Rhizospheric oxidationdisplayed a seasonal trend in Typha latifolia with decreasingoxidation percentages during warmer months as the importance ofrhizospheric CH4 oxidation declined relative toCH4 emission (46.5 ±13.8% in December and 13.5 ±1.7% in July). However, the absolute rateof methane oxidation was highest during the warmer months (44.2± 3.4 mg m-2 d-1 inDecember and 318.7 ± 151.4 mg m-2d-1 in July). As methane emission rates increased,the sensitivity of the methyl fluoride technique decreased dueto the larger error between replicate flux measurements.
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    URL: http://dx.doi.org/10.1023/A:1005750201264
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    Die-back of Phragmites australis: influence on the distribution and rate of sediment methanogenesis (1997)
    Springer
    Biogeochemistry 36 (1997), S. 173-188 
    Details
    ISSN: 1573-515X
    Keywords: die-back ; methane ; methanogenesis ; Phragmites australis ; rhizosphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Methanogenesis was measured during the summer of 1994, in sediment coresand bulk samples from a Phragmites australis wetland in northern Jutland,Denmark. We compared sediment from healthy reed and dying-back reed, andan open lagoon resulting from die-back. Cores revealed variability withdepth and between sites, with the highest rates coinciding with layers oforganic gyttja, and negligible methane production from the underlying sandbase. Methanogenesis rates in the lagoon and die back sites were higher(up to 100–150 nmol h-1 g-1dry wt. sediment) than in the healthy reed (50–80 nmolh-1 g-1), with the highest rates being recordedfrom May to July. At these times, methanogenesis was markedly temperature-limited; samples incubated at 30 °C anon-limiting temperature, gave rates as high as 200–400nmol h-1 g-1 for the lagoon and die-backareas and 150 nmol h-1 g-1 for the healthyarea. Addition of 8 mM acetate and H2/CO2headspace suggested that both acetate-fermenting andCO2-reducing bacteria were present. Acetate additions suggested some co-limitation by substrate availability, with acetate limitation occurring in the healthy site during July and in the die-back site during August. Lower rates during August, especially in the healthy area, were associated with low water levels which resulted in more oxidized sediments. The data reveal highly variable methanogenesis in the sediment which, when considered with sediment depths, indicates that sites of Phragmites die-back have significantly greater rates of anaerobic mineralization than surrounding healthy wetland, and may be intense sources of methane.
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    URL: http://dx.doi.org/10.1023/A:1005761609386
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    Distribution of greenhouse gases, nitrite, and δ13C of dissolved inorganic carbon in Lake Biwa: Implications for hypolimnetic metabolism (1997)
    Springer
    Biogeochemistry 36 (1997), S. 205-221 
    Details
    ISSN: 1573-515X
    Keywords: autochthonous organic matter ; carbon dioxide ; decomposition ; methane ; nitrous oxide ; δ13C
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The vertical distribution of dissolved greenhouse gases (CH4,ΣCO2 and N2O), NO $${\text{NO}}_{\text{2}} - $$ ,and δ13C of ΣCO2 in Lake Biwa during a stagnantperiod was precisely determined. ΣCO2 as well as NO $${\text{NO}}_{\text{3}} - $$ was accumulated in the hypolimnion, whereas NO $${\text{NO}}_{\text{2}} - $$ and CH4concen\-trations were generally higher in theepilimnion than in the hypolimnion. In August, NO $${\text{NO}}_{\text{2}} - $$ andCH4 were ephemerally accumulated at the thermocline. Theconcentration of CH4 always exceeded equilibrium with respectto air/water exchange. N2O was rather uniformly distributed inboth time and space, and remained near equilibrium with respect toair/water exchange. All of these observations are similar to otherstratified, oligotrophic lakes, in which the hypolimnia were welloxygenated. The δ13C of ΣCO2 became morenegative with increasing depth, and showed a strong negativecorrelation with apparent oxygen utilization. From the data, the δ13Cvalue of organic matter decomposed into ΣCO2 inthe hypolimnion was calculated by isotope mass-balance, and found tobe in a similar range to δ13C of phytoplankton and benthic algaeand distinctively higher than δ13C of both terrestrial andsedimentary organic matters. This suggests that autochthonous organicmatter was the major source of ΣCO2.
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    Enzymes and biogeochemical cycling in wetlands during a simulated drought (1997)
    Springer
    Biogeochemistry 39 (1997), S. 177-187 
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    ISSN: 1573-515X
    Keywords: glucosidase ; methane ; peat ; phosphatase ; sulphate ; sulphatase ; wetland
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Possible interactions between soil enzymes and thebiogeochemistry of wetlands were investigated duringa field-based drought simulation. Under control(waterlogged) conditions, correlations were foundbetween the activity of the enzyme B-glucosidase andtwo properties associated with carbon cycling, namelyi) CH4 release r = 0.79,p lt 0.01) and ii) dissolvedorganic carbon concentration (r= -0.81, p lt 0.01). In contrast,the transition to drought conditions resulted in correlations betweenB-glucosidase activity and certain mineralisationprocesses, namely the release of mg and Ca(r = 0.72, p lt 0.05). Sulphataseactivity correlated with changes in sulphate concentration during the droughtsimulation (r = 0.73, p lt 0.05).Further support for the suggested enzymic involvement in biogeochemicalprocesses was found in laboratory studies. Theseexperiments indicated that increasing the abundance ofB-glucosidase could stimulate trace gas emissions(p lt 0.001) and increase the concentration ofmagnesium and calcium (p lt 0.05). Increasedsulphatase abundance caused a suppression of methane emissions(p = 0.053).
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    Animal Consciousness and Ethics in Asia and the Pacific (1997)
    Springer
    Journal of agricultural and environmental ethics 10 (1997), S. 249-267 
    Details
    ISSN: 1573-322X
    Keywords: Animals ; Asia ; consciousness ; Australia ; Hong Kong ; India ; Israel ; Japan ; New Zealand ; The Philippines ; Russia ; Singapore ; Thailand
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Philosophy
    Notes: Abstract The interactions between humans, animals and the environment have shaped human values and ethics, not only the genes that we are made of. The animal rights movement challenges human beings to reconsider interactions between humans and other animals, and maybe connected to the environmental movement that begs us to recognize the fact that there are symbiotic relationships between humans and all other organisms. The first part of this paper looks at types of bioethics, the implications of autonomy and the value of being alive. Then the level of consciousness of these relationships are explored in survey results from Asia and the Pacific, especially in the 1993 International Bioethics Survey conducted in Australia, Hong Kong, India, Israel, Japan, New Zealand, The Philippines, Russia, Singapore and Thailand. Very few mentioned animal consciousness in the survey, but there were more biocentric comments in Australia and Japan; and more comments with the idea of harmony including humans in Thailand. Comparisons between questions and surveys will also be made, in an attempt to describe what people imagine animal consciousness to be, and whether this relates to human ethics of the relationships.
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    Adsorption of methane and ethane, 1. Studies of work function changes of Pt foil. Effect of pressure (1997)
    Springer
    Reaction kinetics and catalysis letters 62 (1997), S. 163-169 
    Details
    ISSN: 1588-2837
    Keywords: Work function change ; adsorption ; methane ; ethane ; Pt foil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Pt work-function changes have been measured on adsorption of methane and ethane at different temperatures in the 10−5–10−2 mbar pressure range. Correlations were found between pressure of hydrocarbons and Pt work function changes.
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    Adsorption of methane and ethane, 2. Studies of metal blacks in a dynamic system (1997)
    Springer
    Reaction kinetics and catalysis letters 62 (1997), S. 171-178 
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    ISSN: 1588-2837
    Keywords: Pt ; Pd ; Rh ; methane ; ethane ; irreversible adsorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The irreversible adsorption of methane and ethane increases with increasing temperature on Pt, Pd and Rh blacks. Data indicate a one-carbon attachment of ethane on Pt and Pd. A two-carbon attachment of ethane is observed upon adsorption on Rh.
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    Adsorption and selectivity of carbon dioxide with methane and nitrogen in slit-shaped carbonaceous micropores: Simulation and experiment (1996)
    Springer
    Adsorption 2 (1996), S. 193-203 
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    ISSN: 1572-8757
    Keywords: mixture adsorption ; cabon dioxide ; methane ; carbon pores ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract We have used the grand canonical Monte Carlo method to study the adsorption and selectivity of mixtures of carbon dioxide with methane and nitrogen at high (i.e., ambient) temperatures in model slit pores with graphitic surfaces. Experimental data, including new high pressure measurements for carbon dioxide and methane on a non-porous graphitic standard, were used to test the potential models. The mixture simulations predict that carbon dioxide is preferentially adsorbed in both systems. The results are discussed in terms of competing energetic and entropic effects and the underlying molecular mechanisms.
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    Promotional effect of Pt on non-oxidative methane transformation over Mo-HZSM-5 catalyst (1996)
    Springer
    Catalysis letters 39 (1996), S. 169-172 
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    ISSN: 1572-879X
    Keywords: methane ; non-oxidative conversion ; platinum/molybdenum/HZSM-5 zeolite
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The influence of modification of Mo-HZSM-5 catalyst by Pt on methane non-oxidative transformation to ethylene and aromatics is investigated. Carbon accumulation on the catalyst is studied by means of DTA and TG methods. It is demonstrated that the addition of Pt to Mo-HZSM-5 considerably enhances the catalyst stability and reduces the carbon deposition on the catalyst. In the meanwhile, Mo-HZSM-5 is shown not to be a good catalyst for methane non-oxidative conversion because the total efficiency for methane conversion to useful products is even lower than it is in the oxidative coupling process.
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    The nature of active sites for the oxidation of methane on La-based perovskites (1996)
    Springer
    Catalysis letters 42 (1996), S. 57-63 
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    ISSN: 1572-879X
    Keywords: perovskites ; methane ; catalytic combustion ; La-carbonate species ; surface carbonates ; explosion method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Highly crystalline, monophasic LaFeO3 and LaCoO3 perovskites, prepared by the explosion method, are shown to be heterogeneous at surface level. The outmost atomic layers of these perovskites contain high concentrations of carbonate-type species. Their specific activities for methane combustion are in fact identical to La2O2CO3 and air-exposed La2O3. These results compared with pertinent data from the literature hint that surface heterogeneity may be often present in mixed oxides catalysts.
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    Reduction of nitric oxide with methane on Pd/Co/H-ZSM-5 catalysts: cooperative effects of Pd and Co (1996)
    Springer
    Catalysis letters 42 (1996), S. 185-189 
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    ISSN: 1572-879X
    Keywords: NO reduction ; methane ; palladium ; cobalt ; H-ZSM-5 zeolite ; cooperative effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Reduction of low concentration of nitric oxide (NO) with methane as a reductant under wet conditions has been investigated using Pd/Co/H-ZSM-5 catalysts and the effects brought about by coexistence of Pd and Co are discussed. The role of Co is attributed to the acceleration of oxidation of NO to NO2, which is the necessary species for reduction of NO with CH4 on Pd sites. A Pd/H-ZSM-5 loading of 1 wt% Co shows a maximum activity for NO reduction as well as for NO oxidation. Excess loading of Co led to a decrease in activity for NO reduction. An XPS study shows that Pd and Co are well dispersed inside the zeolite when the concentrations of Pd and Co are less than 1 wt%. Loading of excess Co, however, causes aggregation of Pd on the surface of ZSM-5.
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    Partial oxidation of methane over platinum metal gauze (1996)
    Springer
    Catalysis letters 36 (1996), S. 25-30 
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    ISSN: 1572-879X
    Keywords: partial oxidation ; Pt metal gauze ; methane ; synthesis gas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The partial oxidation of methane to synthesis gas has been studied over a platinum gauze catalyst. The experiments were carried out at atmospheric pressure with a single gauze in a quartz reactor heated in an electric furnace. The furnace temperature was varied in the range 200–900°C and the space time in the range 0.00021–0.00042 s. The feed consisted of a mixture of CH4∶O2∶Ar≈2∶1∶10 and carbon oxides and water were the main products. Oxygen was only partly consumed and relatively small amounts of hydrogen were formed.
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    CH4/CD4 isotope effects in the carbon dioxide reforming of methane to syngas over SiO2-supported nickel catalysts (1996)
    Springer
    Catalysis letters 38 (1996), S. 77-79 
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    ISSN: 1572-879X
    Keywords: CH4/CD4 isotope effects ; CO2 reforming ; methane ; syngas ; Ni/SiO2 catalyst
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract By performing the CH4 + CO2 and CD4 + CO2 reactions alternately over SiO2-supported nickel catalysts in a pulse micro-reactor, normal deuterium isotope effects on both the methane conversion reaction and on the CO formation reaction have been observed in the process of CO2 reforming of methane. Based on the observed CH4/CD4 isotope effects, the pathways for the formation of CO are discussed.
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    Adsorption of a four-component gas mixture on zeolite NaX (1996)
    Springer
    Russian chemical bulletin 45 (1996), S. 794-796 
    Details
    ISSN: 1573-9171
    Keywords: nitrogen ; methane ; ethane ; propane ; combined adsorption ; zeolite NaX ; selectivity coefficient
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Adsorption of N2, CH4, C2H6, C3H8, and their mixture on zeolite NaX was studied by the volumetric method under static conditions at 278 K in the pressure range from 0.1 to 0.8 MPa. Compressibility factors were calculated in order to take into account the nonideal character of the gas phase. Adsorption isotherms of individual gases and partial isotherms were obtained. The adsorption properties of gases in the adsorption of a mixture and its components were compared. The selectivity coefficient of adsorption of propane in the N2-CH4-C2H6-C3H8-NaX system was calculated, and its dependence on the total pressure was determined.
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    Ab initio study on carbon Kinetic Isotope Effect (KIE) in the reaction of CH4+Cl• (1996)
    Springer
    Journal of atmospheric chemistry 23 (1996), S. 37-49 
    Details
    ISSN: 1573-0662
    Keywords: Ab initio ; methane ; chlorine ; kinetic isotope effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Recent studies suggest that the destruction of methane by Cl• in the marine boundary layer could be accounted for as another major sink besides the methane destruction by OH•. High level ab initio molecular orbital calculations have been carried out to study the CH4+Cl• reaction, the carbon Kinetic Isotope Effect (KIE) is calculated using Conventional Transition-State Theory (CTST) plus Wigner and Eckart semiclassical tunneling corrections. The calculated KIE is around 1.026 at 300 K and has a small temperature variation. This is by far the largest KIE among different processes involving atmospheric methane destruction (e.g., OH•, soil). A calculated mass balance of atmospheric methane including the KIE for the CH4+Cl• reaction is found to favor those methane budgets with enhanced biological methane sources, which have relatively lighter carbon isotope composition.
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    Methane in sulfate-rich and sulfate-poor wetland sediments (1996)
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    Biogeochemistry 34 (1996), S. 57-70 
    Details
    ISSN: 1573-515X
    Keywords: Cladium jamaicense ; Eleocharis spp. ; Typha domingensis ; interstitial water ; methane ; sulfate ; northern Belize
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Wetlands of northern Belize provide a unique opportunity to study methane production and emissions from marshes dominated by identical species (Typha domingensis, Cladium jamaicense) and genus (Eleocharis spp.), but differing substantially in the amount of sulfates present in the sediments. Some marshes occur on limestone marls rich in gypsum (CaSO4) while others are underlain by alluvial sands poor in sulfates. Concentrations of methane and sulfates in the sediment interstitial water are one or more orders of magnitude different for these two geological substrata averaging 139.2 and 14.9 μM of CH4, and 0.08 and 11.53 mM of SO4 −2 2 on alluvial sands and limestone respectively. The amount of methane found in the internal atmosphere of plants from alluvial sands is significantly higher (6.3 μM) than in plants from limestone (0.19 μM). The average methane emissions measured in wetlands located on alluvial sands were 25.2 mg m−2 h−1 while emissions from marshes on limestone were only 2.4 mg m−2 h−1. These values extrapolated for the entire year and the respective wetland areas resulted in the estimate of total CH4 emissions from northern Belize of 0.066 Tg per year.
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    Partial oxidation of methane to synthesis gas on Pt electrode in a solid oxide electrolyte cell (1996)
    Springer
    Reaction kinetics and catalysis letters 58 (1996), S. 407-416 
    Details
    ISSN: 1588-2837
    Keywords: Partial oxidation ; methane ; synthesis gas ; platinum electrode-catalyst ; solid oxide electrolyte cell
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The partial oxidation of methane to synthesis gas or oxyreforming of methane over a Pt electrode in a solid oxide electrolyte cell $$CH_4 + O_2 ,Pt\left| {ZrO_2 (10 mol \% Y_2 O_3 )} \right|Pt,air$$ has been studied under open and closed circuit conditions. Experiments were performed at atmospheric pressure over a temperature range of 700–800°C and methane/oxygen ratios of 0.4–1.8. The Pt electrode was found to be an active electrode-catalyst for oxyreforming of methane and electrochemical oxidation of the oxyreforming products. The mechanism of methane oxyreforming and the effect of anodic current passing through the cell on the catalytic properties of the Pt electrode for oxyreforming of methane are discussed.
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    Combustion of methane over supported palladium-copper bimetallic catalysts (1996)
    Springer
    Reaction kinetics and catalysis letters 59 (1996), S. 253-262 
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    ISSN: 1588-2837
    Keywords: Catalytic combustion ; methane ; palladium ; copper oxide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Monometallic and bimetallic catalysts based on palladium and copper deposited on a spinel carrier have been investigated in the catalytic combustion of methane. Great differences were found in catalytic activity, according to the sequence Pd/MgAl2O4〉CuO−Pd/MgAl2O4〉Pd−CuO/MgAl2O4〉CuO/MgAl2O4. They were explained by changes in surface composition of the catalysts. In the case of bimetallic catalysts the metallic surface is preferentially enriched in copper, which acts as a diluting agent for the Pd atom ensembles. As a consequence, the adsorption of reactants is limited and the catalysts so obtained behave like copper slightly doped with palladium.
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    Study of cool-Dame phenomena during self-ignition of methane-oxygen mixtures (1996)
    Springer
    Russian chemical bulletin 45 (1996), S. 2316-2320 
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    ISSN: 1573-9171
    Keywords: methane ; oxidation ; cool names ; kinetic simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Experimental studies and kinetic simulation have shown that the formation of cool flames is as typical of oxidation of methane as of oxidation of its homologs. Phenomena peculiar to the cool-flame processes in closed systems are observed, namely, the region of a negative temperature coefficient of the reaction, single and double cool-flame flashes, two stage ignition, and light radiation in the range of luminescence of formaldehyde.
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    Dehydrogenation of methane on supported molybdenum oxides. Formation of benzene from methane (1995)
    Springer
    Catalysis letters 32 (1995), S. 43-53 
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    ISSN: 1572-879X
    Keywords: methane ; benzene ; MoO3/SiO2
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The dehydrogenation of methane on MoO3 supported on various oxides has been investigated under non-oxidizing conditions in a fixed bed, continuous flow reactor. Detailed measurements were performed with MoC3/SiO2. The reaction of methane was observed above 923 K after a significant time lag, when a partial reduction of Mo6+ occurred, the reduced phase being characterized by X-ray photoelectron spectroscopy (XPS). The initial gaseous products are CO2, H2O, H2 and CO. But this stage is followed by the dehydrogenation of methane and coupling of hydrocarbon fragments to various hydrocarbons. A possible pathway of the formation of benzene, the main product of reaction with selectivities ranging from 26 to 56%, is suggested.
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    In situ FTIR study on the active oxygen species for the conversion of methane to methanol (1995)
    Springer
    Catalysis letters 35 (1995), S. 259-263 
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    ISSN: 1572-879X
    Keywords: FT-IR ; oxygen species ; methane ; methanol ; iron aluminum phosphate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In situ FTIR studies showed the generation of a peroxide species by the contact of a H2-O2 gas mixture or of N2O with Fe-Al-P-O catalysts at ⩾573 K. This oxygen species oxidized methane into methanol at ⩾473 K, through the formation of methoxide species on the catalysts.
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    X-ray photoelectron spectroscopy of Pd/γ-alumina and Pd foil after catalytic methane oxidation (1995)
    Springer
    Catalysis letters 34 (1995), S. 31-40 
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    ISSN: 1572-879X
    Keywords: palladium ; PdO ; alumina ; methane ; oxidation ; carbon ; XPS ; ellipsometry ; structure sensitivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Samples of palladium supported onγ-alumina and a palladium foil were used as catalysts for methane oxidation at 550° C. The samples were quenched quickly in the reaction chamber to room temperature in flowing Ar and then transferred in vacuo for XPS analysis. Structure sensitivity was manifest from an increase in PdO stability and a decrease in carbon deposition relative to Pd with increasing particle size. The results were compared with recent ellipsometric data.
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    Suppression of carbon deposition in CO2-reforming of methane on metal sulfide catalysts (1995)
    Springer
    Catalysis letters 35 (1995), S. 39-43 
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    ISSN: 1572-879X
    Keywords: carbon deposition ; CO2-reforming ; methane ; metal sulfide ; supported Ni
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The catalytic performance of metal sulfides of Mo and W was studied for the CO2-reforming of methane by comparing with that of Ni/SiO2. The sulfide catalysts have lower activity than the Ni/SiO2 catalyst for this reaction, however, no deactivation due to carbon deposition was observed on the sulfide catalysts. The activity for direct decomposition of CH4 was much smaller on the sulfides than on supported Ni. The rate equation suggested that, during steady-state reaction, the surface was abundant in adsorbed CO2 on sulfides, by which direct decomposition of CH4 should be retarded in addition to their lower activity for this reaction.
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  • 98
    Electronic Resource
    Electronic Resource
    Interaction of methane with surfaces of silica, aluminas and HZSM-5 zeolite. A comparative FT-IR study (1995)
    Springer
    Catalysis letters 35 (1995), S. 245-258 
    Details
    ISSN: 1572-879X
    Keywords: methane ; adsorption ; hydroxyl groups ; H-D exchange reaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Infrared investigations on the interaction of methane with silica, aluminas (η,γ and α) and HZSM-5 zeolite have been carried out. At low temperature (173 K), methane adsorption was observed over these oxides and HZSM-5 zeolite. Our findings featured that the infrared inactiveΝ 1 band (2917 cm−1) of a gaseous methane molecule became active and shifted to lower frequencies (2900 and 2890 cm−1) when it adsorbed on the surfaces of these adsorbents. Our results also demonstrate that hydroxyl groups played a very important role in methane adsorption over the acidic oxides and the HZSM-5 zeolite. When interaction between the hydroxyl groups and methane took place, the band shift of the hydroxyl groups varied with different oxides. The strength of the interaction decreased according to the following sequence, Si-OH-Al〉Al-OH〉Si-OH, which is in accordance with the order of their acidities. At higher temperatures, methane interacted quite differently with various oxides and HZSM-5 zeolite. It has been observed that the hydroxyl groups of silica, γ-alumina and HZSM-5 zeolite could exchange with CD4 at temperatures higher than 773K, while those on η-alumina could exchange at a temperature as low as 573 K. Another interesting observation was the formation of formate species over Al2O3 (both η and γ) at temperatures higher than 473 K. The formate species would decompose to CO2, or produce carbonate at much higher temperatures. Formation of formate species was not observed over silica and HZSM-5 under similar conditions, α-Al2O3 did not adsorb or react with methane in any case.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00807180
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  • 99
    Electronic Resource
    Electronic Resource
    Carbon monoxide induced desorption of alkanes and alkenes up to C8 after chemisorption of methane on platinum (1995)
    Springer
    Catalysis letters 31 (1995), S. 19-26 
    Details
    ISSN: 1572-879X
    Keywords: methane ; chemisorption ; methane chemisorption ; methane oligomerization ; precursors of higher hydrocarbons ; hydrocarbonaceous adspecies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract CH4 homologation can proceed under reductive conditions by successive exposures of various supported metals to CH4 and H2. When a Pt/SiO2 catalyst is submitted to a CO dose after an exposure to CH4 at a moderate temperature, several hydrocarbons are released with a large proportion of olefins. It may therefore be concluded that C-C bonding processes take place during the mere exposure of platinum to CH4 at moderate temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00817029
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  • 100
    Electronic Resource
    Electronic Resource
    Oxidative coupling of methane on silver catalysts (1995)
    Springer
    Catalysis letters 32 (1995), S. 185-194 
    Details
    ISSN: 1572-879X
    Keywords: methane ; silver ; oxidative coupling ; C2 selectivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Bulk silver catalysts were found to be active for the oxidative coupling of methane to ethane and ethylene if operated under oxygen-limited conditions at atmospheric pressure and at temperatures above 1020 K. The addition of small amounts of sodium phosphate as promoter increases markedly the C2 selectivity (to values above 90%) and yield (〉10%) by efficient suppression of reaction steps leading to total oxidation. Further improvement of the yields might be achieved by more appropriate reactor design.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00806113
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