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题名: 矿质氧化物表面硫酸盐、硝酸盐和铵盐的生成机制研究
作者: 杨卫卫
学位类别: 博士
答辩日期: 2016-05
授予单位: 中国科学院研究生院
授予地点: 北京
导师: 贺泓
关键词: 矿质氧化物,非均相反应,复合效应,SNA,灰霾形成
其他题名: A laboratory study for the formation mechanism of sulfate, nitrate and ammonium (SNA) on mineral dust
学位专业: 环境科学
中文摘要:     近三十年来随着我国中东部工业化和城市化程度的加深,灰霾天气现象出现乃至频发,成为我国面临的主要环境问题之一。二次无机气溶胶的形成,尤其是硫酸盐、硝酸盐和铵盐  (SNA)的爆发式增长是灰霾形成的重要因素。矿质颗粒物作为全球排放通量较高的一类气溶胶颗粒,其表面具有的金属离子、羟基、表面氧、缺陷位和表面吸附水等是大气中痕量气体吸附和转化的重要活性位点,是SNA非均相形成的重要场所。因此探究矿质氧化物表面的非均相反应过程对探究灰霾的成因具有重要的意义。本论文采用原位漫反射红外光谱(DIRFTS)和流动管反应器(Flow tube  reactor),并借助离子色谱(IC)、X光电子能谱(XPS)、程序升温脱附(TPD)和场发射扫描电镜(FE-SEM)及透射电镜(TEM)等其他相关的技术手段在实验室范围内系统的研究了矿质氧化物表面 SNA非均相形成过程,并提出了可能的反应机制。
    首先研究了 SO2在不同结构、形貌和表面性质的氧化物表面的非均相反应过程。DRIFTS结果发现氧化物的酸碱性、氧化还原性与表面生成物种的吸附构型和吸附量密切相关,其中在酸性的 SiO2、Al2O3、TiO2表面生成微量的亚硫酸盐;在碱性的 MgO、CaO表面有亚硫酸盐生成,并在    MgO表面有明显的硫酸盐产生;在过渡性 Fe2O3和MnO2表面则生成的是硫酸盐。离子色谱定量分析结果显示,氧化物表面总硫含量为金属氧化物 MnO2 (217.14μg g-1m-2) >过渡金属氧化物α-Fe2O3 (187.45μg g-1m-2 )>碱性的    MgO (140.03 μg g-1m -2 )>酸性的TiO2(62.01 μgg-1m-2 )>酸性的γ-Al2O3 (20.24μgg-1 m-2)。氧化物的形貌结构将影响SO2的吸附形态和摄取量。以  MnO2为例,结晶度差、比表面和孔体积较大的纳米线组成的球状结构的 γ-和 δ-MnO2表面主要生成聚合态的硫酸盐物种;而结晶度较高、比表面积和孔体积较小的树枝状结构的α-和β-MnO2表面主要生成双齿硫酸盐,其中 SO2在晶格氧含量最高的δ-MnO2表面摄取系数最高,达(1.48 ±0.21) ×10-6。因此,为了更好的认识大气颗粒物的非均相化学,模型颗粒物的选择须考虑表面化学性质和物理结构的影响,尤其是过渡金属氧化物的催化氧化对硫酸盐的生成可能具有重要的作用。
    其次考察了 NH3共存对SO2非均相反应过程的影响,发现SO2和NH3在矿质氧化物表面存在复合效应。在酸性的 γ-Al2O3、TiO2表面,NH3存在主要促进了亚硫酸盐的生成;在碱性的 MgO和氧化还原性质的α-Fe2O3表面,则主要促进了硫酸盐的生成。对 NH3而言,SO2共存促使其由  Lewis酸位点的配位NH3+转化为 Brønsted酸位点的吸附NH4+,并且极大的提高了其生成量。SO2和 NH3的复合效应在酸性氧化物表面更明显。进一步考察了水汽对SO2和NH3在γ-Al2O3、α-Fe2O3表面非均相反应过程的影响。结果表明,H2O的存在改变了SO2和NH3的吸附形态和吸附量。在α-Fe2O3表面,湿度的提高降低了  SO2和   NH3的吸附量,并且由于 NH3的吸附受抑制,表面碱性降低,致使硫酸盐向硫酸氢盐转变。在γ-Al2O3表面,水汽通入导致吸附态的亚硫酸盐向水溶性的亚硫酸盐和水溶性的硫酸盐转化;同时,NH3的吸附随着相对湿度的提高而显著降低。离子色谱结果显示 SO2和NH3之间的复合效应随着湿度的提高而减弱,这可能由于  H2O覆盖了表面活性位点,抑制了酸碱复合物“+ H4N—SO32-”的形成。
       最后,在前期研究基础上,初步考察了低浓度(1 ppmv)条件下,SO2、NO2和NH3单独或共存时在氧化物表面的非均相反应过程。不同于比表面积过低的α-Al2O3和碱性的CaO和MgO,NO2和NH3在α-Fe2O3表面存在明显的复合效应。碱性氧化物表面,SO2和  NO2共存较NO2 + NH3或SO2+NH3显著提高了SO42- 和 NO3-的生成;酸性氧化物表面尽管 NO3-的生成规律不变,然SO42-的生成在 SO2+NH3条件下较SO2+NO2条件下更明显。 SO2+NH3较 NO2+NH3明显促进了 NH4+的形成。两两复合效应可能存在竞争机制,因为三种气氛共存对表面产物的生成促进并不明显。富 NH3情况下,表面 SO42-和 NO3-的生成大大增强。
英文摘要:        In  recent thirty  years,  with  the development  of  China's industrialization,  haze pollution occurs frequently,  which has become one  of the most severe  environmental problems. The production  of secondary inorganic aerosols, i.e.  the explosive increase of sulfate, nitrate and ammonium, affects the haze formation significantly. Mineral dust represents  the largest  fraction  of atmospheric  particulate  matter (APM),  which  can promoted the formation of SNA by providing metal ions, OH, surface oxygen,  defects and adsorbed water etc. Research on the heterogeneous reactions on those mineral dusts is  important  to   explore  the  haze  formation   mechanism.  In  this dissertation,   the heterogeneous reactions of SO2/NH3/NO2 on  typical mineral oxides were investigated using DRIFTS, flow tube  reactor, and other techniques,  such as IC, XPS,  TPD, TEM and FE-SEM; possible mechanisms were also proposed.
     Firstly, the  individual reaction  of SO2  on mineral  oxides with  different surface properties and  morphologies was  investigated. DRIFTS results  show that  adsorption configuration and amount of  surface products have a close relationship  with the acid-base and redox properties. On  acid SiO2, Al2O3 and TiO2, SO2 adsorbed mainly in  the form of sulfite; on base MgO and CaO, sulfite species formed though sulfate were also found on MgO. SO2 mainly converted into sulfate on transition-metal oxides. IC results showed that the adsorption amount of SO2 decreased  in the order of MnO2 (217.14 μgg-1m-2)>α-Fe2O3 (187.45μg g -1m-2 )>MgO (140.03μg g-1m-2)> TiO2 (62.01μg g-1m-2)>γ-Al2O3 (20.24 μg  g-1m-2).Phase  structure and  morphologies of  oxideswill influence the adsorption  form and uptake amount  of SO2. For instance, γ-  and δ-MnO2 with spherical nanostructures composed of nanowires show high uptake for SO2(mainly oxidized into  poly-sulfate) due to poor crystallinity,  large BET area and pore volume. In contrast, α- and β-MnO2 with dendritic nanostructures show low uptake for SO2 (mainly oxidized into bidentate sulfate) due to  perfect crystallinity, low BET area and pore volume. The SO2 obtained the largest uptake coefficient on δ-MnO2 with (1.48± 0.21) ×10-6. Therefore, surface chemical properties and physical structure need to be taken  into  account  in  the  choice  of  model  particles  for  better  understanding  the heterogeneous atmospheric  chemistry.  Particularly, the  catalytic  oxidation ability  of transition-metal oxides might count for the formation of sulfate species.
    Then, a  synergistic effect  between  SO2 and  NH3 on  mineral oxides  was found during the  heterogeneous reactions. The  presence of NH3  promoted the formation of sulfite  on  acid  γ-Al2O3  and  TiO2  while  sulfate  on  base  MgO  and  α-Fe2O3.   SO2 coexistence altered  the adsorption form  of NH3, which  transformed from Lewis  acid site-coordinated NH3 to Brønsted acid site-bound NH4+ and the adsorption amount also enhanced during this process. It was found that H2O influenced  the adsorption state of SO2 and NH3 on γ-Al2O3 and α-Fe2O3. On α-Fe2O3, the adsorption amount of SO2   and NH3 decreased with  increasing RH; and sulfate converted  to bisulfate due to  lowered surface basicity by decreased adsorption of NH3. On γ-Al2O3, H2O led to the conversion of  adsorbed sulfite  species to  water-solvated  sulfite and  sulfate,  and NH3  was  also inhibited to  adsorb with RH. IC  results show that  the synergistic effect  between SO2 and NH3 was  weakened as the RH increased  possibly because available reactive sites on the surface  were blocked by adsorbed  water and then the  donor-acceptor complex “+H4N—SO32-” was inhibited to form.
     Finally, the heterogeneous reactions  of SO2, NO2 and NH3  at low concentrations (1 ppmv) were investigated. NO2  and NH3 was found to react more synergistically  on α-Fe2O3 than that on  α-Al2O3 as well as base CaO and MgO. Compared  to SO2+NO2,NO2+NH3 or SO2+NH3 were weak in promoting the formation of SO42- or NO3-on base CaO and MgO. However, in the  case of SO42-, the promotion effect by SO2+NO2   and SO2+NH3 shows the reverse result on acid α-Fe2O3 and α-Al2O3. SO2+NH3  contributed to  the formation  of  NH4+  more  significantly than  NO2+NH3.  Each  two synergistic effects, such  as NO2+NH3  and SO2+NO2  may compete  with each  other, because  no promotion effect for the formation of surface  products was found when SO2, NO2  and NH3 coexisted in  the gas flow. Large amount  of SO42-   and  NO3-  was induced to form under NH3-rich condition.
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/37035
Appears in Collections:大气污染控制中心_学位论文

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Recommended Citation:
杨卫卫. 矿质氧化物表面硫酸盐、硝酸盐和铵盐的生成机制研究[D]. 北京. 中国科学院研究生院. 2016.
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