SO2和NO对ACF低温脱除模拟燃煤烟气中VOC的影响

采用H₂O₂浸渍的方法对活性炭纤维(ACF)进行改性,并利用氮吸附等温线和XPS(X-ray photoelectron spectroscopy)的方法对ACF样品进行表征。通过实验测定改性前后ACF脱除VOC(甲苯作为VOC的代表物)的效果,同时考察二氧化硫(SO₂)和一氧化氮(NO)对ACF脱除甲苯的影响。研究发现,双氧水浸渍改性对ACF的BET表面积和孔容没有影响,但使得ACF样品表面的含氧官能团含量大量增加。实验数据也表明,SO₂和NO对VOC在ACF上的吸附具有抑制作用,且随着两者浓度的增加,抑制作用也增强。 研究还发现,SO₂和NO同时存在比单一的SO₂或NO对VOC在ACF上吸附的抑制作用更为明显。     

活性炭催化氧化脱除单质汞的研究

模拟煤气的气氛,在硫化氢（H₂S）和氧气（O₂）存在条件下,对活性炭催化氧化吸附单质汞（Hg⁰）的性能进行了研究。结果表明,H₂S和O₂存在条件下,活性炭对Hg⁰的吸附能力明显提高。在180min内,H₂S和O₂共存气氛下,脱汞效率约为78%;只有H₂S存在下,脱汞效率约为69%;没有H₂S和O₂气氛下活性炭脱汞效率快速下降为28%。随着吸附温度的升高,入口汞浓度的提高和吸附剂粒径的增大,活性炭的脱汞效率会随着下降。通过XRD表征表明,Hg⁰的吸附反应机理是Hg⁰在活性炭催化氧化下与H₂S形成硫化汞（HgS）,从而实现了Hg⁰的稳定化脱除。     

NO与NO2在ZnO表面吸附的密度泛函理论研究

采用 DMol ³ 模块中广义梯度密度泛函理论(GGA)的Perdew-Burke-Ernzerh(PBE)方法研究含能材料分解气体产物NO, NO₂在ZnO(10 \bar{1} 0)表面的吸附和NO₂解离生成NO和O的过程. 结果表明, 优化后的吸附构型显示Zn顶位为稳定吸附位点, NO₂的吸附能大于NO. 态密度图分析结合差分电荷密度图表明, NO的N原子与表面Zn有相互作用, 电荷从NO转移到表面; NO₂的N_2p, O_2p轨道与表面Zn_3d轨道发生杂化, NO₂附近积累大量负电荷. 过渡态搜索显示NO₂的解离需跨过较高能垒, 不易进行.     

复杂烟气条件下太西活性焦脱除Hg0的实验研究

为了解复杂烟气条件下活性焦吸附剂的脱汞特性,利用汞渗透管和主要气体成分模拟复杂烟气,在实验室规模的固态吸附剂汞吸附效能测定系统上,进行了太西活性焦吸附单质汞的实验研究,并采用FT-IR对活性焦表面进行了光谱表征。结果表明,在活性焦表面存在各种含氧官能团;在CO₂/N₂/O₂/SO₂/Hg⁰烟气体系中,当SO₂加入量为400、855、1 520 mL/m³时,出口汞浓度分别为36、43、48 μg/m³,SO₂对系统吸附Hg⁰的能力有抑制作用;在CO₂/N₂/O₂/NO/Hg⁰烟气体系中,较低浓度的NO对Hg⁰脱除有抑制作用,而高浓度值的NO抑制作用减弱;在CO₂/N₂/O₂/NO/SO₂/Hg⁰烟气体系下,提高NO浓度对Hg⁰脱除有一定的促进作用,而提高SO₂浓度初期促进汞的脱除,后期则表现为抑制作用。     

甲烷在氧化铁表面还原NO的特性与反应机理研究

在程序控温电加热水平陶瓷管反应器中,在300~1 050 ℃,对N₂气氛中甲烷在氧化铁(充分氧化后的铁丝网卷)表面还原NO的特性进行了实验研究,测试了NO脱除效率、CO生成量以及反应后铁样品表面组分和微观状态的变化特点,分析了甲烷在氧化铁表面还原NO的反应机理。在此基础上,在1 000 ℃时,对模拟烟气条件下甲烷在氧化铁表面还原NO的持久性进行了实验研究。结果表明,甲烷在氧化铁表面能够高效地还原NO。在N₂气氛下,在850 ℃以上达到100%的NO脱除效率。在模拟烟气中,甲烷在氧化铁表面脱除NO的能力具有很好的持久性。实验结果表明,在1 000 ℃时,采用由体积分数为2.0%的O₂、16.8%的 CO₂和524×10^-6的 NO,N₂配平的模拟烟气,1.17% CH₄能够在连续100 h内保持100%的NO脱除效率,而未出现下降的趋势。对反应机理的研究结果表明,甲烷在氧化铁表面还原NO的机理包括甲烷通过再燃机理还原NO以及甲烷通过在氧化铁表面还原氧化铁为金属铁、金属铁进而直接还原NO两种主要反应机理。其中,后者为主要反应机理。     

In/HZSM-5催化剂上CH4选择还原NO机理研究

考察了CH⁴+O₂,NO+CH₄(+O₂)与NO₂+CH₄(+O₂)反应体系中CH₄的转化活性.结果表明,浸渍法制备的In/HZSM₅催化剂上CH₄选择还原NO过程中,NO₂的形成起到了活化甲烷的作用.根据NO和NO₂在In/HZSM₅与HZSM₅样品上的TPD及IR研究结果,认为在载体HZSM₅的酸性位及In/HZSM₅催化剂的活性中心In位上均可形成NO₂,NO₂与CH₄的反应在In位上进行.     

微波放电脱除NO

报道一种不用催化剂,一步脱除NO的新方法--常压微波放电法。探讨在(NO,He),(NO.O₂,He)和(NO,O₂,H₂O,He)体系中微波放电脱除NO的差异。研究结果表明,在(NO,He)条件下可实现一步高效脱除NO,在(NO,O₂,He)条件下也可实现80%左右的NO转化,其中N₂的选择性高达80%,而H₂O的加入并未影响N₂的产率。同时发现,随着微波功率的加大,NO转化率也增大,而N₂的选择性增大得更多。最终可达到一个平衡值。最后研究了NO和O₂浓度及气体流量对NO脱除的影响。     

活性炭纤维催化氧化NO的量子化学研究

利用密度泛函理论的B3LYP方法,6-31G(d)基组,在zigzag型的四并苯模型上对NO、O2分子在活性炭纤维(ACFs)表面的吸附行为进行研究,并探讨了ACFs催化氧化NO的主要机理路径。研究结果表明,环境气氛中的O2分子可以先吸附于ACFs表面形成两个半醌基(C-O),之后C-O和吸附态的NO(C-NO)发生氧化反应生成-NO2;游离态的O2也可以经过ACFs表面的催化作用形成活性氧原子(O*)从而直接和吸附态的NO反应生成-NO2。与NO相比,O2分子的吸附能大,在同NO的竞争吸附中占据优势,结合统计热力学分析,吸附态的NO和游离态的O2所产生的活性氧原子发生氧化反应是NO转化为NO2的主要途径。     

沥青基球状活性炭担载尿素用于NO2的低温选择性催化还原行为研究

将作为还原剂的尿素担载于沥青基球状活性炭(PSAC)上研究了NO₂的低温选择性催化还原(SCR)反应。结果表明,PSAC上尿素担载量的提高可以增大NO₂与尿素的反应几率;当尿素担载量由8%提高到30%时,SCR反应脱硝活性显著提高,脱硝时间相应延长。在30~90℃,升高反应温度会减小NO₂在PSAC表面的吸附量,从而导致NO_x的脱除量减小。增加反应气氛中NO₂和O₂的浓度均有利于脱硝活性的提高,但当O₂进料浓度大于9%时,继续增加O₂进料浓度对脱硝活性的改善作用变得微弱。降低空速有利于提高脱硝活性和延长脱硝时间。当反应温度为30℃、空速为2000h^-1、NO₂和O₂的进料浓度分别为0.05%和21%时,尿素担载量为8%的PSAC可在49h内实现85%以上的NO_x转化率。     

Ag-ZSM-5催化剂上CH4选择催化还原NOx的研究

摘要研究Ag-ZSM-5催化剂上CH₄选择性催化还原NO_x的反应性能,采用TPD和TPSR技术研究NO和O₂共吸附于Ag-ZSM-5催化剂表面形成的吸附物种及其和CH₄之间的反应。结果表明,Ag-ZSM-5催化剂上CH₄选择性还原NO_x活性和选择性较高。NO和O₂共吸附在Ag-ZSM-5催化剂上形成的NO₃(s)吸附物种能被CH₄还原生成N₂.在NO₃(s)和O₂共存的体系中,CH₄能优先并选择性还原NO₃(s)生成N₂.     

Influence of oxygen plasma treatment on hydrogen chloride removal of activated carbon fibers

The oxygen plasma treatment of activated carbon fibers (ACFs) was carried out to introduce oxygen-containing groups onto carbon surfaces. Surface properties of the ACFs were determined by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). N2/77 K adsorption isotherms were investigated by BET and D-R plot methods to characterize specific surface area, pore volume, and pore size distribution. The efficiency of hydrochloride removal was confirmed by two kinds of methods; one is detecting tubes (range: 1-40 ppm), and the other is a gas chromatography technique. As experimental results, the hydrochloride removal efficiency of the ACFs was increased with the number of plasma treatment times up to around 300%, resulting from newly formed oxygen-containing functional groups (especially phenolic and carboxylic) on carbon surfaces, in the decreased specific surface areas or pore volumes. These results indicate that the plasma treatment leads to the increase of hydrochloride removal due to the improvement of surface functional groups containing oxygen on the carbon surfaces.     

Effect of carbon surface modification with dimethylamine on reactive adsorption of NO(x)

The wood-based activated carbon, either as received or oxidized with nitric acid, was exposed to dimethylamine vapors. This modification was expected to introduce nitrogen groups. Then, the modified samples were used as adsorbents of NO(2) under dynamic conditions. Both NO(2) breakthrough curves and the NO concentration curves were recorded. The samples before and after exposure to NO(2) were characterized using adsorption of nitrogen, elemental analysis, potentiometric titration, FTIR, and thermal analysis. Modifications with amines resulted in an increase in NO(2) adsorption and in a decrease in NO emission. The effects were more visible when oxidation was used as a pretreatment of the carbon surface. This process increased the incorporation of nitrogen to the carbon matrix via acid-based reactions resulting in the formation of amides and amine carboxylic salts. Besides this, dimethylamine was strongly adsorbed on the carbon surface via hydrogen bonding with oxygen-containing groups. When the samples were exposed to nitrogen dioxide, there was an indication that nitramine and nitrosoamine were formed in the reactions of NO(2) with either amides or amines. In the reactions of amines with NO, nitrosoamines are the likely products. As a next step, the surface of the carbon matrix is reoxidized by NO(2), which is accompanied by the release of NO.     

Adsorption of ammonia and water on functionalized edge-rich carbon nanofibers

The preparation, characterization and ammonia and water adsorption properties of edge-rich carbon nanofibers (CNFs) were studied, including platelet CNFs (PCNFs) and cup-stacked CNFs (CSCNFs). Since PCNFs and CSCNFs have many chemically active exposed edges, functionalization by oxidizing the edges was carried out by ozone stream and by nitric acid. Transmission electron microscopy, N₂ adsorption isotherms and temperature-programmed desorption analysis showed that the nitric acid treatment partly destroyed the graphite structure of the PCNFs and created acid functional groups and micropores, whereas the ozone treatment created functional groups without damaging the structure. Ammonia adsorption isotherms clarified that NH₃ adsorption on PCNFs and CSCNFs occurred mainly on oxygen-containing groups, whereas the adsorption on activated carbon fibers (ACFs) occurred on both oxygen-containing groups and the carbon surface without the functional groups, and the CSCNFs showed larger amounts of adsorbed ammonia compared to the PCNFs. Especially at a relatively low pressure range (<0.2 atm), the PCNFs/CSCNFs/ACFs showed the same ammonia adsorption mechanism; that is, the one-to-one interaction between oxygen atoms in the functional groups and hydrogen atoms in ammonia molecules. In addition, the adsorption on the ACFs appeared to occur mainly by interaction with the carbon surface at relatively high pressure (0.3–1.0 atm). Our experimental results and previous findings suggest that NH₃ adsorption on PCNFs is due mainly to NH…O hydrogen bonding between oxygen-containing groups and ammonia rather than to chemical bonding.     

Analysis of functional groups on the surface of plasma-treated carbon nanofibers

Plasma chemically modified carbon nanofibers were characterized by X-ray photoelectron spectroscopy with regard to the content of carbon, oxygen, and nitrogen and the contribution of carboxylic groups or ester, carbonyl and hydroxylic groups or ether on the surface. Unfortunately, X-ray photoelectron spectroscopy only provides an average value of the first 10 to 15 molecular layers. For comparison, depth profiles were measured and wet chemical methods were applied to estimate the thickness of the functionalized layer and the distribution of oxygen-containing functional groups within the near-surface layers. The results indicate that the fiber surface is covered by a monomolecular oxygen-containing layer and that plasma treatment allows a complete oxygen functionalization of the uppermost surface layer. The best conditions for plasma treatment found within the set of parameters applied to generate complete functionalization are: plasma gas O(2)/Ar ratio 1:1, gas pressure 1-1.5 hPa, plasma power 80 W, treatment time >or= 5 min. Additionally, three quick and easy methods are presented to estimate the efficiency of plasma treatment with regard to surface functionalization: pyrolysis, contact angle measurements, and light permeability measurements of aqueous carbon nanofiber suspensions.     

乙烯渣油沥青基活性炭纤维和粘胶基活性炭纤维的表面性质与脱硫活性

研究了在O2和H2O存在下,乙烯渣油沥青基活性炭纤维(ETPACF)和粘胶基活性炭纤维(CelluloseACF)的脱硫活性.结果表明,在比表面积相近的情况下,ETPACF的脱硫活性明显低于CelluloseACF,这可归因于后者具有较强的吸附和催化氧化SO2能力及较大的吸水量,尤其是具有较强的催化氧化SO2的能力,这些能力又与其表面含有含氮官能团以及某些含氧官能团有关,因此ACF的表面官能团对其脱硫活性影响很大.     

Ammonia removal of activated carbon fibers produced by oxyfluorination

In this study, activated carbon fibers (ACFs) were produced by an oxyfluorination treatment to enhance the capacity of ammonia gas removal. The introduction of polar groups, such as CF, CO, and COOH, on the ACFs was confirmed by a XPS analysis, and N2/77 K adsorption isotherm characteristics including specific surface area and total and micropore volumes were studied by the BET and t-plot methods. The ammonia-removal efficiency was confirmed by a gas-detecting tube technique. As a result, the specific surface area and micropore volume of ACFs were slightly destroyed as the surface treatment time was increased. However, the oxyfluorinated ACFs led to an increase of fluorine and oxygen-containing polar functional groups in ACF surfaces, resulting in an increase in the ammonia-removal efficiency of the ACFs produced.     

Low Temperature Catalytic Hydrolysis of Carbon Disulfide on Activated Carbon Fibers Modified by Non-thermal Plasma

In order to improve the carbon disulfide (CS₂) catalytic hydrolysis efficiency of activated carbon fibers (ACFs), ACFs surface was modified by non-thermal plasma (NTP). In particular, the effects of modification conditions on the catalyst properties were studied, including the reactor structure, modification atmosphere, modification time, output voltage and discharge gap. The catalytic activity study showed that ACFs with NTP modification enhanced CS₂ catalytic hydrolysis. The optimal reactor structure, modification atmosphere, modification time, output voltage and discharge gap was a coaxial cylinder, an N₂ atmosphere, 5 min, 7 kV and 7.5 mm, respectively. The effect of the NTP modification on the micro-structural properties of the ACFs was characterized using scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) and X-ray photoelectron spectroscopy (XPS) methods. The results showed that NTP modification improved the dispersion of functional groups and increased the number of oxygen-containing and nitrogen-containing functional groups, thus the catalytic activity could be enhanced. The present results indicated that NTP modification was an effective way to manipulate ACFs surface properties for the CS₂ catalytic hydrolysis reaction.     

Photochemistry of adsorbed nitrate

In the atmosphere, gas-phase nitrogen oxides including nitric acid react with particle surfaces (e.g., mineral dust and sea salt aerosol) to yield adsorbed nitrate, yet little is known about the photochemistry of nitrate on the surface of these particles. In this study, nitrate adsorbed on alumina surfaces, a surrogate for mineral dust aerosol, is irradiated with broadband light (lambda > 300 nm) in the absence and presence of coadsorbed water, at <1% and 45 +/- 2% relative humidity (%RH), respectively, and molecular oxygen. Upon irradiation, the nitrate ion readily undergoes photolysis to yield nitrogen-containing gas-phase products, NO2, NO, and N2O. Although NO2, NO, and N2O form under the different conditions investigated, both coadsorbed water and molecular oxygen change the gas-phase product distribution, with NO being the major product under dry and humid conditions in the absence of molecular oxygen and NO2 the major product in the presence of molecular oxygen. To the best of our knowledge, this is the first study to investigate the role of solvation by coadsorbed water in the photochemistry of adsorbates at solid interfaces and the roles that molecular oxygen, adsorbed water, and relative humidity may have in photochemical processes on aerosol surfaces that have the potential to alter the chemical balance of the atmosphere.     

硫化氢对活性炭脱除单质汞的影响

H₂S是煤气中的含硫成分,活性炭能否催化氧化煤气中的H₂S形成活性硫,以促进H₂S和Hg⁰的协同脱除是值得研究的。 本文首先通过程序升温脱附和热力学分析了低温情况下H₂S对活性炭脱除Hg⁰的影响。 在较低吸附温度130 ℃下,H₂S不仅不能作为硫源,还使活性炭对Hg⁰的吸附显著减弱,这主要是由于H₂S对活性炭表面的吸附氧的消耗以及H₂S对含氧官能团的氧的取代反应造成的。 在此基础上,进一步研究了高温下H₂S对活性炭的影响,高温也不能使活性炭有效渗入单质硫。 所以无论低温还是高温情况下,利用H₂S作为硫源使Hg⁰以HgS的形式脱除并不是活性炭脱汞的可行手段。 本文揭示了较宽的温度范围内H₂S对单纯的活性炭脱除Hg⁰的影响机理,能为用于煤气脱汞的活性炭的设计以及作为负载时机理研究提供支持作用。