Direct decomposition of NO activated by microwave discharge

The environmentally friendly removal of NO has been investigated using continuous microwave discharge (CMD) at atmospheric pressure. In these experiments, conversions of NO to N-2 as well as NO2 were mainly observed for both dry and wet feed gas, which showed a great difference from those observed with other discharge methods. The effects of a series of reaction parameters, including microwave input power, O-2 concentration, NO concentration, and gas flow rate, on the product distribution and energy efficiency were also studied. Under all reaction conditions, the conversions of NO to N-2 were higher than those to NO2. The highest conversion of NO to N-2 was 88%. The reaction rate of NO removal and the effects of the different discharge modes on NO conversion and product distribution are also discussed. Through comparison of the results of different discharge modes, it was found that the addition of CH4 apparently increased the conversion of NO to N-2 as well as the energy efficiency. A possible reaction process is suggested.

大气CH_4中碳稳定同位素组成的PreCon-GC/C-IRMS系统测定

利用预浓缩装置-气相色谱/燃烧-同位素比值质谱仪(PreCon-GC/C-IRMS)联用系统,建立了就采样、浓缩和在线质谱分析大气CH4中稳定碳同位素组成的测定方法。通过多组试验对比,分析并讨论了利用PreCon-GC/C-IRMS联用技术测定大气CH4中碳稳定同位素比值的试验条件、系统线性、稳定性及准确度和精密度等。结果表明,在本研究方法条件下,当离子流强度在1.0~20 V时,系统线性良好(斜率S=0.04‰/V),在4.0~15 V内其线性(斜率S=0.03‰/V)优于总体线性;系统测量稳定性可靠,δ13C值的测定结果的S.D<0.3‰,最大偏差<0.5‰,回收率达99.99%,准确度和精度均符合分析与研究要求。利用该系统对室内和室外草坪地空气中CH4的碳稳定同位素组成做初步测试,其碳同位素的平均值分别为-31.358‰和-33.085‰,且相同地点区域空气中CH4的1δ3C值,在1 d内和不同日期间的变化均在0.5‰以内,重现性良好。

稻田CH_4和N_2O排放关系及其微生物学机理和一些影响因子

用静态箱法原位观测和分析了我国北方稻田 3～ 1 2月CH4和N2 O的排放及其关系 ,并研究了这一关系发生的微生物学机理 .同时 ,监测了土壤湿度、pH、水分及Eh的变化 .结果表明 ,稻田CH4和N2 O排放之间存在着互为消长的关系 (R2 =0 0 4 94) .土壤湿度、pH及Eh变化范围分别在 0～ 2 4℃、6 87～ 7 0 2和 41 5～ 30 0mv之间 ,水分从非淹水期的 38～ 72 %FC至 5～ 1 0cm浅水淹灌 .土壤Eh对CH4和N2 O的释放起重要的调控作用 .在整个观测期内 ,与CH4和N2 O释放密切相关的 6种菌群 (发酵细菌、产氢产乙酸细菌、产甲烷细菌、甲烷氧化菌、硝化细菌、反硝化细菌 )各有其数量消长及酶活性变化规律 ,稻田CH4和N2 O排放之间互为消长的关系受这些相关微生物数量及酶活性变化的共同调控 .

Direct conversion of methane under nonoxidative conditions

Direct conversion of methane into hydrogen and valuable chemicals under nonoxidative conditions is a process severely limited thermodynamically. However, the movement from the present era of fossil fuels into the coming hydrogen energy age makes it an interesting and important approach compared with the direct conversion of methane under the aid of oxidants. This paper gives a brief overview of the direct conversion of CH4 under nonoxidative conditions. At the same time, our understanding of methane dehydroaromatization over Mo/HZSM-5 catalysts for the simultaneous formation of hydrogen and light aromatics is discussed in general, while the bifunctionality of Mo/HZSM-5 catalysts and the role of carbonaceous deposits formed during the reaction are reviewed in more detail. A perspective of the topic from both academic points of view and potential industrial applications is also presented. (C) 2003 Elsevier Science (USA). All rights reserved.

In situ FT-IR spectroscopic studies of CO adsorption on fresh Mo2C/Al2O3 catalyst

The surface sites of supported molybdenum carbide catalyst derived from different synthesis stages have been studied by in situ FT-IR spectroscopy using CO as the probe molecule. Adsorbed CO on the reduced passivated Mo2C/Al2O3 catalyst gives a main band at 2180 cm(-1), which can be assigned to linearly adsorbed CO on Mo4+ sites. The IR results show that the surface of reduced passivated sample is dominated by molybdenum oxycarbide. However, a characteristic IR band at 2054 cm-1 was observed for the adsorbed CO on MoO3/Al2O3 carburized with CH4/H-2 mixture at 1033 K (fresh Mo2C/Al2O3), which can be assigned to linearly adsorbed CO on Modelta+ (0 < delta < 2) sites Of Mo2C/Al2O3, Unlike adsorbed CO on reduced passivated Mo2C/Al2O3 catalyst, the IR spectra of adsorbed CO on fresh Mo2C/Al2O3 shows similarity to that on some of the group VIII metals (such as Pt and Pd), suggesting that fresh carbide resembles noble metals. To study the stability Of Mo2C catalyst during H-2 treatment and find proper conditions to remove the deposited carbon species, H-2 treatment of fresh Mo2C/Al2O3 catalyst at different temperatures was conducted. Partial amounts of carbon atoms in Mo2C along with some surface-deposited carbon species can be removed by the H, treatment even at 450 K. Both the surface-deposited carbon species and carbon atoms in carbide can be extensively removed at temperatures above 873 K.

Shape selectivity in methane dehydroaromatization over Mo/MCM-22 catalysts during a lifetime experiment

Dehydroaromatization of CH4 with 2% CO2 on 6Mo/MCM-22 in a 100-h lifetime test was carried out at 993 K, atmospheric pressure and 1500 mL/gh. The duration of the lifetime test can be divided into an induction stage, stable stage and deactivation stage on the basis of the selectivities of hydrocarbons and coke. The characteristics of deposited coke with different time onstream were studied using TPO and TG techniques. There were two peaks corresponding to two kinds of coke recorded in TPO profiles, and the oxidation temperature of coke shifted to higher values with less hydrogen content with the increase of coke deposits. BET and Benzene-TPD techniques were employed to study the variation of specific surface area of the external and micropore surface versus time onstream. With the accumulation of coke deposits, although the pores became partially blocked and the internal surface decreased, methane could still enter the channel and was converted to benzene with shape selectivity until a critical value of coke deposition was reached.

A Mossbauer study of In-Fe2O3/HZSM-5 catalysts for the selective catalytic reduction of NO by methane

The selective catalytic reduction of NO by CH4 was compared over In-Fe2O3/HZSM-5 catalysts prepared by impregnation and co-impregnation methods. It was found that the catalyst preparation method greatly affected the catalyst activity. The impregnated catalyst was very active, but the co-impregnated one showed poor activity. The In Fe2O3/HZSM-5 catalysts were investigated by Mossbauer spectroscopy. The results showed that indium cations entered into the iron oxide lattice in the co-impregnated catalyst, while the impregnated catalyst exhibited a more stable structure, when both of the catalysts were treated severely in the reaction atmosphere. Characterization by means of combined in situ temperature programmed reduction (TPR)- Mossbauer spectroscopy further revealed that the performances of the two catalysts were different in the TPR processes.

Controls on suppression of methane flux from a peat bog subjected to simulated acid rain sulfate deposition

The effect of acid rain SO42− deposition on peatland CH4 emissions was examined by manipulating SO42− inputs to a pristine raised peat bog in northern Scotland. Weekly pulses of dissolved Na2SO4 were applied to the bog over two years in doses of 25, 50, and 100 kg S ha−1 yr−1, reflecting the range of pollutant S deposition loads experienced in acid rain-impacted regions of the world. CH4 fluxes were measured at regular intervals using a static chamber/gas chromatographic flame ionization detector method. Total emissions of CH4 were reduced by between 21 and 42% relative to controls, although no significant differences were observed between treatments. Estimated total annual fluxes during the second year of the experiment were 16.6 g m−2 from the controls and (in order of increasing SO42− dose size) 10.7, 13.2, and 9.8 g m−2 from the three SO42− treatments, respectively. The relative extent of CH4 flux suppression varied with changes in both peat temperature and peat water table with the largest suppression during cool periods and episodes of falling water table. Our findings suggest that low doses of SO42− at deposition rates commonly experienced in areas impacted by acid rain, may significantly affect CH4 emissions from wetlands in affected areas. We propose that SO42− from acid rain can stimulate sulfate-reducing bacteria into a population capable of outcompeting methanogens for substrates. We further propose that this microbially mediated interaction may have a significant current and future effect on the contribution of northern peatlands to the global methane budget.

Characterization of stable isotope fractionation during methane production in the sediment of a eutrophic lake,lake dagow,germany

We measured delta C-13 of CO2, CH4, and acetate-methyl in profundal sediment of eutrophic Lake Dagow by incubation experiments in the presence and absence of methanogenic inhibitors chloroform, bromoethane sulfonate (BES), and methyl fluoride, which have different specificities. Methyl fluoride predominantly inhibits acetoclastic methanogenesis and affects hydrogenotrophic methanogenesis relatively little. Optimization of methyl fluoride concentrations resulted in complete inhibition of acetoclastic methanogenesis. Methane was then exclusively produced by hydrogenotrophic methanogenesis and thus allowed determination of the fractionation factors specific for this methanogenic pathway. Acetate, which was then no longer consumed, accumulated and allowed determination of the isotopic signatures of the fermentatively produced acetate. BES and chloroform also inhibited CH4 production and resulted in accumulation of acetate. The fractionation factor for hydrogenotrophic methanogenesis exhibited variability, e. g., it changed with sediment depth. The delta C-13 of the methyl group of the accumulated acetate was similar to the delta C-13 of sedimentary organic carbon, while that of the carboxyl group was by about 12 parts per thousand higher. However, the delta C-13 of the acetate was by about 5 parts per thousand lower in samples with uninhibited compared with inhibited acetoclastic methanogenesis, indicating unusual isotopic fractionation. The isotope data were used for calculation of the relative contribution of hydrogenotrophic vs. acetoclastic methanogenesis to total CH4 production. Contribution of hydrogenotrophic methanogenesis increased with sediment depth from about 35% to 60%, indicating that organic matter was only partially oxidized in deeper sediment layers.

阔叶红松林土壤CO_2,N_2O排放和CH_4吸收的研究(英文)

为研究凋落物对CO2,N2O排放和CH4吸收的影响,从2002年9月3日到2003年10月30日,采用静态密闭箱技术对长白山阔叶红松林两种类型土壤生态系统的CO2,N2O和CH4的通量进行测定。两种土壤类型分别为表层有凋落物覆盖和没有凋落物覆盖。研究结果表明,凋落物对CO2,N2O和CH4通量有显著性影响(P<0.05)。有凋落物样地的CO2,N2O和CH4通量的日变化趋势和无凋落物样地中三种气体的日变化趋势相似,且CO2,N2O和CH4的日通量峰值都出现在18:00。有凋落物样地的CO2,N2O和CH4通量的季节变化趋势和无凋落物样地中三种气体的季节变化趋势也相似,但在一年之中,CO2和CH4的峰值出现在六月,N2O的峰值却出现在八月。研究结果还表明有凋落物样地CO2,N2O的日排放通量和年均排放通量明显大于无凋落物样地中两种气体的排放通量,但有凋落物样地的CH4日吸收通量和年均排放通量却小于无凋落物样地的CH4吸收通量。

沈阳市排污明渠——细河CH_4的排放

利用封闭箱法测定了沈阳市排污明渠———细河水面CH4 的排放通量 ,结果表明 ,细河是重要的CH4 排放源 ,水面全年有甲烷排放 ,排放通量达到 2 80 .8mg·m-2 ·d-1.且明显受水温和水体污染物影响 ,即夏季高 ,冬季低 ;渠首高 ,渠尾低 ;以细河作为排污明渠处置污水 ,每升污水的甲烷贡献率为 0 .36 6mg ,高于普通二级污水处理厂 .

土壤溶解性有机碳(DOC)的影响因子及生态效应

土壤溶解性有机碳(DOC)是陆地生态系统中极为活跃的有机组分,是土壤圈层与相关圈层(如生物圈、大气圈、水圈和岩石圈等)发生物质交换的重要形式。影响土壤中物质的溶解、吸附、解吸、吸收、迁移乃至生物毒性等行为之外,对温室气体CH4的排放、水体水质的污染、岩石圈的风化等的影响也不可忽视。本文以陆地生态系统的中的DOC为主体,探讨了DOC的生态环境意义及其对大气、水体和岩石圈的影响以及DOC对土壤管理措施的响应。

下辽河平原稻田非生长季碳排放观测研究

应用静态箱 /气相色谱法对下辽河平原稻田非生长季碳排放动态变化规律进行了测定。结果表明 ,非生长季 (10月至翌年 4月 )稻田CH4、CO2 和N2 O排放总体上随气温变化而发生变化。在冻融期 (3月中下旬 )CO2 和N2 O有明显的排放。非生长季节的稻田是大气CO2 和N2 O的源 ,作为大气CH4的源或汇的作用不明显。

影响土壤N_2O排放和CH_4吸收的主控因素的研究(英文)

本文于2000年7月,在实验室模拟条件下,以长白山阔叶红松林鲜土壤为对象,采用正交试验设计法对土壤进行培养实验,研究了影响土壤N2O排放和CH4吸收的主要因素。考察了温度、水分、pH值、NH4+及NO3-五因素对森林土壤N2O排放和CH4吸收的影响。实验结果显示:在本试验设计的因素、水平条件下,N2O排放速率、CH4吸收速率二者均与土壤pH值和温度这两个因素呈显著正相关。并且N2O排放速率与CH4吸收速率间呈显著线性正相关关。

N2O fluxes from the native and grazed semi-arid steppes and their driving factors in Inner Mongolia, China

This paper presents results of 2 years (from January 2005 to December 2006) of measurement of N2O fluxes from the native and grazed Leymus chinensis (LC) steppes in Inner Mongolia, China using the static opaque chamber method. The measurement was at a frequency of twice per month in the growing season and once per month in the non-growing season. In addition, the possible effect of water-heat factors on N2O fluxes was statistically analyzed. The results indicated that there were distinct seasonal patterns in N2O fluxes with large fluxes in spring, summer, and autumn but negative fluxes in winter. The annual net emission of N2O ranging from 0.24 to 0.30 kg N2O-N ha(-1) and from 0.06 to 0.26 kg N2O-N ha(-1) from the native and grazed LC steppe, respectively. Grazing activities suppressed N2O production. In the growing season, soil moisture was the primary driving factor of N2O fluxes. The high seasonal variation of N2O fluxes was regulated by the distribution of effective rainfall, rather than precipitation intensity. Air temperature or soil temperature at 0, 5, and 10 cm depth was the most restricting factor of N2O fluxes in the non-growing season.