ch4 oxidation
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Author(s):  
Yudong Li ◽  
Jingkai Jiang ◽  
Michael Hinshelwood ◽  
Shiqiang Zhang ◽  
Peter Bruggeman ◽  
...  

Abstract In this work, we investigated atmospheric pressure plasma jet (APPJ)-assisted methane oxidation over a Ni-SiO2/Al2O3 catalyst. We evaluated possible reaction mechanisms by analyzing the correlation of gas phase, surface and plasma-produced species. Plasma feed gas compositions, plasma powers, and catalyst temperatures were varied to expand the experimental parameters. Real-time Fourier-transform infrared spectroscopy (FTIR) was applied to quantify gas phase species from the reactions. The reactive incident fluxes generated by plasma were measured by molecular beam mass spectroscopy (MBMS) using an identical APPJ operating at the same conditions. A strong correlation of the quantified fluxes of plasma-produced atomic oxygen with that of CH4 consumption, and CO and CO2 formation implies that O atoms play an essential role in CH4 oxidation for the investigated conditions. With the integration of APPJ, the apparent activation energy was lowered and a synergistic effect of 30% was observed. We also performed in-situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) to analyze the catalyst surface. The surface analysis showed that surface CO abundance mirrored the surface coverage of CHn at 25 oC. This suggests that CHn adsorbed on the catalyst surface as an intermediate species that was subsequently transformed into surface CO. We observed very little surface CHn absorbance at 500 oC, while a ten-fold increase of surface CO and stronger CO2 absorption were seen. This indicates that for a nickel catalyst at 500 oC, the dissociation of CH4 to CHn may be the rate-determining step in the plasma-assisted CH4 oxidation for our conditions. We also found the CO vibrational frequency changes from 2143 cm-1 for gas phase CO to 2196 cm-1 for CO on a 25 oC catalyst surface, whereas the frequency of CO on a 500 oC catalyst was 2188 cm-1. The change in CO vibrational frequency may be related to the oxidation of the catalyst.


Author(s):  
Jintao Sun ◽  
Qi Chen ◽  
Baoming Zhao ◽  
Caohui Guo ◽  
Jianyu Liu ◽  
...  

Abstract Ion chemistry with temperature evolution in weakly ionized plasma is important in plasma-assisted combustion and plasma-assisted catalysis, fuel reforming, and material synthesis due to its contribution to plasma generation and state transition. In this study, the kinetic roles of ionic reactions in nanosecond discharge (NSD) plasma-assisted temperature-dependent decomposition and oxidation of methane are investigated by integrated studies of experimental measurements and mathematical simulations. A detailed plasma chemistry mechanism governing the decomposition and oxidation processes in a He/CH4/O2 combustible mixture is proposed and studied by including a set of electron impact reactions, reactions involving excited species, and ionic reactions. A zero-dimensional model incorporating the plasma kinetics solver ZDPlasKin and the combustion chemical kinetics solver CHEMKIN is used to calculate the time evolution of the ion density. Uncertainty analysis of ionic reactions on key species generation is conducted by using different referenced data, and insignificant sensitivity is found. The numerical model is consistent with experimental data for methane consumption and generation of major species including CO, CO2, and H2. By modeling the temporal evolution of key ions, it is observed that O2+ presents the largest concentration in the discharge stage, followed by CH4+, CH3+, and CH2+, which is in accordance with the traditional ion chemistry in hydrocarbon flames and agrees well with molecular-beam mass spectrometer investigations. The path flux shows that the concentrations of key species, including electrons, O, OH, H, O(1D), O2(a1Δg), O2+, CH3+, and CH4+, change within 1–2 orders of magnitude and that the transition from a homogeneous state to a contracted/constricted state does not occur. The path flux and sensitivity analysis reveal the significant roles of cations in the stimulation of active radical generation, including CH, O, OH, and O(1D), thus accelerating methane oxidation. This work provides a deep insight into the ion chemistry of temperature-dependent plasma-assisted CH4 oxidation.


2021 ◽  
Vol 9 (11) ◽  
pp. 1261
Author(s):  
Jing Li ◽  
Xiaoqing Xu ◽  
Changling Liu ◽  
Nengyou Wu ◽  
Zhilei Sun ◽  
...  

Aerobic methane (CH4) oxidation plays a significant role in marine CH4 consumption. Temperature changes resulting from, for example, global warming, have been suggested to be able to influence methanotrophic communities and their CH4 oxidation capacity. However, exact knowledge regarding temperature controls on marine aerobic methane oxidation is still missing. In this study, CH4 consumption and the methanotrophic community structure were investigated by incubating sediments from shallow (Bohai Bay) and deep marine environments (East China Sea) at 4, 15, and 28 °C for up to 250 days. The results show that the abundance of the methanotrophic population, dominated by the family Methylococcaceae (type I methanotrophs), was significantly elevated after all incubations and that aerobic methane oxidation for both areas had a strong temperature sensitivity. A positive correlation between the CH4 oxidation rate and temperature was witnessed in the Bohai Bay incubations, whereas for the East China Sea incubations, the optimum temperature was 15 °C. The systematic variations of pmoA OTUs between the Bohai Bay and East China Sea incubations indicated that the exact behaviors of CH4 oxidation rates with temperature are related to the different methanotrophic community structures in shallow and deep seas. These results are of great significance for quantitatively evaluating the biodegradability of CH4 in different marine environments.


ACS Catalysis ◽  
2021 ◽  
pp. 13066-13076
Author(s):  
Junjie Chen ◽  
Kevin Giewont ◽  
Eric A. Walker ◽  
Jungkuk Lee ◽  
Yubiao Niu ◽  
...  
Keyword(s):  

2021 ◽  
Vol 9 (10) ◽  
pp. 2080
Author(s):  
Edda M. Rainer ◽  
Christophe V. W. Seppey ◽  
Caroline Hammer ◽  
Mette M. Svenning ◽  
Alexander T. Tveit

Rising temperatures in the Arctic affect soil microorganisms, herbivores, and peatland vegetation, thus directly and indirectly influencing microbial CH4 production. It is not currently known how methanotrophs in Arctic peat respond to combined changes in temperature, CH4 concentration, and vegetation. We studied methanotroph responses to temperature and CH4 concentration in peat exposed to herbivory and protected by exclosures. The methanotroph activity was assessed by CH4 oxidation rate measurements using peat soil microcosms and a pure culture of Methylobacter tundripaludum SV96, qPCR, and sequencing of pmoA transcripts. Elevated CH4 concentrations led to higher CH4 oxidation rates both in grazed and exclosed peat soils, but the strongest response was observed in grazed peat soils. Furthermore, the relative transcriptional activities of different methanotroph community members were affected by the CH4 concentrations. While transcriptional responses to low CH4 concentrations were more prevalent in grazed peat soils, responses to high CH4 concentrations were more prevalent in exclosed peat soils. We observed no significant methanotroph responses to increasing temperatures. We conclude that methanotroph communities in these peat soils respond to changes in the CH4 concentration depending on their previous exposure to grazing. This “conditioning” influences which strains will thrive and, therefore, determines the function of the methanotroph community.


Author(s):  
Fleur A E Roland ◽  
Alberto V Borges ◽  
Steven Bouillon ◽  
Cédric Morana

Abstract While the emissions of methane (CH4) by the natural systems have been widely investigated, the aquatic sinks are still poorly constrained. Here, we investigated CH4 cycle and its interactions with nitrogen (N), iron (Fe) and manganese (Mn) cycles in the oxic-anoxic interface and deep anoxic waters of a small, meromictic and eutrophic lake, during two summertime sampling campaigns. Anaerobic CH4 oxidation (AOM) was measured from the temporal decrease of CH4 concentrations, with addition of 3 potential electron acceptors (NO3–, iron oxides (Fe(OH)3) and manganese oxides (MnO2)). Experiments with addition of either 15N-labeled nitrate (15N-NO3–) or 15N-NO3– combined with sulfide (H2S), to measure denitrification, chemolithotrophic denitrification and anaerobic ammonium oxidation (anammox) rates were also performed. Measurements showed AOM rates up to 3.8 µmol CH4 L–1 d–1 that strongly increased with the addition of NO3– and moderately increased with the addition of Fe(OH)3. No stimulation was observed with MnO2 added. Potential denitrification and anammox rates up to 63 and 0.27 µmol N2 L–1 d–1, respectively, were measured when only 15N-NO3– was added. When H2S was added, both denitrification and anammox rates increased. Altogether, these results suggest that prokaryote communities in the redoxcline are able to efficiently use the most available substrates.


2021 ◽  
Vol 18 (11) ◽  
pp. 3505-3527
Author(s):  
Peter M. J. Douglas ◽  
Emerald Stratigopoulos ◽  
Sanga Park ◽  
Dawson Phan

Abstract. There is growing interest in developing spatially resolved methane (CH4) isotopic source signatures to aid in geographic source attribution of CH4 emissions. CH4 hydrogen isotope measurements (δ2H–CH4) have the potential to be a powerful tool for geographic differentiation of CH4 emissions from freshwater environments, as well as other microbial sources. This is because microbial δ2H–CH4 values are partially dependent on the δ2H of environmental water (δ2H–H2O), which exhibits large and well-characterized spatial variability globally. We have refined the existing global relationship between δ2H–CH4 and δ2H–H2O by compiling a more extensive global dataset of δ2H–CH4 from freshwater environments, including wetlands, inland waters, and rice paddies, comprising a total of 129 different sites, and compared these with measurements and estimates of δ2H–H2O, as well as δ13C-CH4 and δ13C–CO2 measurements. We found that estimates of δ2H–H2O explain approximately 42 % of the observed variation in δ2H–CH4, with a flatter slope than observed in previous studies. The inferred global δ2H–CH4 vs. δ2H–H2O regression relationship is not sensitive to using either modelled precipitation δ2H or measured δ2H–H2O as the predictor variable. The slope of the global freshwater relationship between δ2H–CH4 and δ2H–H2O is similar to observations from incubation experiments but is different from pure culture experiments. This result is consistent with previous suggestions that variation in the δ2H of acetate, controlled by environmental δ2H–H2O, is important in determining variation in δ2H–CH4. The relationship between δ2H–CH4 and δ2H–H2O leads to significant differences in the distribution of freshwater δ2H–CH4 between the northern high latitudes (60–90∘ N), relative to other global regions. We estimate a flux-weighted global freshwater δ2H–CH4 of −310 ± 15 ‰, which is higher than most previous estimates. Comparison with δ13C measurements of both CH4 and CO2 implies that residual δ2H–CH4 variation is the result of complex interactions between CH4 oxidation, variation in the dominant pathway of methanogenesis, and potentially other biogeochemical variables. We observe a significantly greater distribution of δ2H–CH4 values, corrected for δ2H–H2O, in inland waters relative to wetlands, and suggest this difference is caused by more prevalent CH4 oxidation in inland waters. We used the expanded freshwater CH4 isotopic dataset to calculate a bottom-up estimate of global source δ2H–CH4 and δ13C-CH4 that includes spatially resolved isotopic signatures for freshwater CH4 sources. Our bottom-up global source δ2H–CH4 estimate (−278 ± 15 ‰) is higher than a previous estimate using a similar approach, as a result of the more enriched global freshwater δ2H–CH4 signature derived from our dataset. However, it is in agreement with top-down estimates of global source δ2H–CH4 based on atmospheric measurements and estimated atmospheric sink fractionations. In contrast our bottom-up global source δ13C-CH4 estimate is lower than top-down estimates, partly as a result of a lack of δ13C-CH4 data from C4-plant-dominated ecosystems. In general, we find there is a particular need for more data to constrain isotopic signatures for low-latitude microbial CH4 sources.


2021 ◽  
Author(s):  
Yasuyuki Yamada ◽  
Kentaro Morita ◽  
Takuya Sugiura ◽  
Yuka Toyoda ◽  
Nozomi Mihara ◽  
...  

<div><div><div><p>Herein, we report that the close-stacking of a double-decker-type dinuclear iron phthalocyanine complex on a graphite surface is effective for achieving high methane oxidation activity, comparable to those of certain MMOs, in an aqueous solution. </p></div></div></div>


2021 ◽  
Author(s):  
Yasuyuki Yamada ◽  
Kentaro Morita ◽  
Takuya Sugiura ◽  
Yuka Toyoda ◽  
Nozomi Mihara ◽  
...  

<div><div><div><p>Herein, we report that the close-stacking of a double-decker-type dinuclear iron phthalocyanine complex on a graphite surface is effective for achieving high methane oxidation activity, comparable to those of certain MMOs, in an aqueous solution. </p></div></div></div>


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