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锰基氧化物上含氧挥发性有机污染物催化氧化过程研究
Alternative TitleStudies on catalytic oxidation process of oxygen-containing volatile organic compounds on manganese-based oxide catalysts
孙永刚
Subtype博士
Thesis Advisor郝郑平
2019-06
Degree Grantor中国科学院生态环境研究中心
Place of Conferral北京
Degree Name工学博士
Degree Discipline环境工程
Keyword锰基氧化物,Ovocs,动力学,反应机理 manganese-based Oxide, Ovocs, Kinetics, Reaction Mechanism
Abstract

      针对挥发性有机污染物(VOCs)的排放与控制,探究重点行业及重点有机污染物在高效催化材料上的反应过程、机理及动力学行为意义重大。本研究主要依据包装印刷行业典型含氧挥发性有机污染物(OVOCs)的排放特征,设计并制备了高效的锰基氧化物催化体系。针对性的考察了其对乙醛、异丙醇、丙酮和乙酸乙(烯)酯等及其混合组分在内的典型OVOCs的催化氧化性能,研究了催化材料与OVOCs间的构效关系,探究了典型OVOCs催化氧化的过程、机理和动力学行为,并提出了锰基氧化物催化体系上OVOCs高效氧化去除的普适性规律。主要研究结果及结论如下:
      (1) MnxAlO催化剂上醛酮氧化反应过程与机理研究
      研究了系列CoAlO、FeAlO、NiAlO和MnAlO类水滑石复合氧化物体系上醛酮类OVOCs的催化氧化过程及反应机理,结果表明MnAlO对乙醛(T100<150℃)和丙酮(T100<170℃)展现出优异的催化活性和高的CO2选择性。优异的低温氧化还原性能和表面丰富的-□-Mn4+-O2-缺陷位及酸结构位点有效的促进了污染物分子吸附活化,水汽实验表明,竞争吸附导致水分子对醛酮催化活性呈现出部分可逆的影响。
      系列不同Mn/Al摩尔比实验结果表明,Mn3AlO(Mn/Al=3)材料表面存在丰富固有的以及形成型的缺陷位,从而引发其结构单元[MnO6]中Mn-O键的弱化,进一步增强了污染物分子和氧分子的吸附活化和解离以及活性氧物种的产生。通过反应过程和机理的研究,结果表明包括η1(O)(ads)、CH2=C(CH3)=O(ads)、O*、CH3CHO*、CH2O*和COO(ads)等在内的中间物种或过渡态在丙酮催化过程中起到关键作用,其α-H的脱除和氧分子的解离活化引发了反应的高效进行,随后-C-C-断裂和CH2O*物种分解使其完全矿化为CO2和H2O,其中-C-C-的断裂是反应的速控步骤。
      (2) MnO2基催化材料上乙酸乙烯酯的催化氧化过程与机理研究
      基于不同[MnO6]结构单元键和方式形成的MnO2晶体结构差异性特征,分别制备了具有一维棒状结构(OMS-2、β-MnO2、γ-MnO2),二维片层结构(δ-MnO2)和非晶结构(AMO)的系列MnO2催化剂用于乙酸乙烯酯的催化氧化,活性结果表明:OMS-2 (隧道结构纳米棒,T90=151℃) > AMO (非晶态,T90=164℃) > δ-MnO2 (层状结构,T90=182℃),其中一维孔道结构材料活性表明:OMS-2 (2×2) > γ-MnO2 (2×1, 1×1) > β-MnO2 (1×1)。活性差异源于OMS-2催化剂拥有更多的氧空位和可利用的表面氧物种、[MnO6]结构单元Mn-O键的弱化和Mn3+/Mn4+氧化还原对有利于活性氧物种的迁移和转化。反应机理表明,低温下(T<60℃)酯键的断裂引发包括乙醛、乙酸、甲酸和烯醇互变异构体等中间物种的产生,促进反应高效进行,其中MnO2材料表面共边键和的[MnO6]结构单元Mn-O键的弱化是关键的活性位点,该特征可有效催化氧化其他典型OVOCs(乙醛、丙酮、异丙醇和乙酸乙酯等)污染物。
      (3) 锰基氧化物上多组分OVOCs的催化氧化反应过程及动力学行为研究
研究了OMS-2催化剂上典型OVOCs(乙醛、丙酮和乙酸乙酯)的催化氧化反应过程及动力学行为。结果表明内外传质过程不会影响催化反应动力学行为,高浓度污染物在高转化率阶段对反应活性影响更大。三类污染物在催化氧化过程中存在相互抑制作用,其中低浓度丙酮对乙醛氧化性能抑制现象更为明显,乙醛和丙酮之间的竞争吸附作用强于乙醛和乙酸乙酯。Power-rate law动力学模型和Mars-van Krevelen动力学模型均适用于其反应过程的模拟,其中Mars-van Krevelen动力学模型能更好的预测乙酸乙酯的催化氧化

Other Abstract

      In view of the emission and control of volatile organic pollutants (VOCs), it is of great significance to explore the reaction process, mechanism and kinetic behavior of key industries and organic pollutants on high-efficiency catalytic materials. In this thesis work, based on the emission characteristics of typical oxygenated volatile organic pollutants (OVOCs) in the packaging and printing industry, a highly efficient manganese-based oxide catalyst system was designed and prepared, the catalytic oxidation properties of typical OVOCs, such as acetaldehyde, isopropanol, acetone and ethyl acetate, and their mixed components were investigated, and the structure-activity relationship between catalytic materials and OVOCs was revealed. Finally, the reaction mechanism and kinetic behavior of typical OVOCs catalytic oxidation were elaborated, and the universality rule of efficient removal of OVOCs over manganese-based oxide catalyst system was proposed. The main findings and conclusions are as follows:
      (1) MnxAlO catalysts for acetone and acetaldehyde catalytic oxidation
      The catalytic performance and reaction mechanism of acetone and acetaldehyde over a series of CoAlO, FeAlO, NiAlO and MnAlO hydrotalcite-derived oxides systems were studied, respectively. Detailed results showed that the excellent catalytic activity for acetaldehyde (T100<150°C) and acetone (T100<170°C), and high CO2 selectivity over MnAlO catalyst were observed. Superior low-temperature redox properties, abundant surface -□-Mn4+-O2- defects and acid structure sites can effectively promote the adsorption and activation of OVOCs and oxygen molecules. The water vapor experiments shown that negative effect of water vapor on distribution of by-product and catalytic activity was observed due to the competitive process.
      The experimental results of different Mn/Al molar ratios show that Mn3AlO(Mn/Al=3) catalyst has abundant inherent and formative defects, which leads to the weakening of Mn-O bond in the structural unit [MnO6] and enhances the adsorption and dissociation of acetone and oxygen molecules, and promote the production of reactive oxygen species. Furthermore, in situ DRIFT and theoretical calculations was adopted to explore the reaction mechanism. The η1(O)(ads), CH2=C(CH3)=O(ads), O*, CH3CHO*, CH2O* and COO(ads) were considered as the main intermediate species and/or transient state during the reaction progress. It was revealed that the acetone and oxygen molecules was activated by the dehydrogenation step (α-H abstraction) and dissociation process, respectively, subsequently, the breaking of -C-C- bonds and CH2O decomposion was occurred, yielding H2O and CO2 via the COO- adsorbed species. Particularly, -C-C- bond breaking was the main limiting step for acetone oxidation.
      (2) Catalytic performance and reaction mechanism of vinyl acetate over different crystal structures manganese dioxides
       Based on the difference of [MnO6] structural unit in crystal structure of MnO2, the one-dimensional rod structure MnO2 (OMS-2, β-MnO2, γ-MnO2), two-dimensional lamellar structure (δ-MnO2) and non-crystal structure (AMO) were prepared, respectively. The sequence of catalytic activity OMS-2 (T90=151oC) > AMO (T90=164 oC) > δ-MnO2 (T90=182 oC), for the one-dimensional MnO2, OMS-2 (2×2) > γ- MnO2 (2×1, 1×1) > β-MnO2 (1×1), the difference in catalytic activity dervied from that the OMS-2 catalyst has more oxygen vacancies, available surface oxygen species, weakening Mn-O bond of the [MnO6] structural unit, and Mn3+/Mn4+ redox pair. The reaction mechanism indicates that the breaking of the ester bond at low temperature (T<60°C) was occurred, it can induce to the the formation of intermediate species including acetaldehyde, acetic acid, formic acid and enol tautomer. Wherein, the weakening of the edge-sharing Mn-O bond in structural unit [MnO6] is a key active site, which can effective to catalytic oxidation of other typical OVOCs (acetaldehyde, acetone, isopropanol and ethyl acetate).
       (3) Studies on the reaction process and kinetic behavior of multicomponent OVOCs over manganese-based oxide catalyst
The catalytic oxidation process and kinetic behavior of typical OVOCs (acetaldehyde, acetone and ethyl acetate) on OMS-2 catalyst were investigated.Detailed results shown that the internal and external mass transfer process does not affect on the kinetic behavior, and the high concentration of pollutants has a greater impact on the reaction performance at the high conversion stage, the mutual inhibition was occurred for the three types of pollutants over OMS-2 catalyst. It is more obvious for mutual inhibition between acetaldehyde and acetone catalytic oxidation, the competitive adsorption between acetaldehyde and acetone is stronger than that of acetaldehyde and ethyl acetate. Both of the Power-rate law kinetic model and the Mars-van Krevelen kinetic model are suitable for the simulation of the reaction process, particularly, the Mars-van Krevelen kinetic model can better predict the catalytic oxidation process of ethyl acetate.
 

Pages168
Language中文
Document Type学位论文
Identifierhttp://ir.rcees.ac.cn/handle/311016/42288
Collection环境纳米技术与健康效应重点实验室
Recommended Citation
GB/T 7714
孙永刚. 锰基氧化物上含氧挥发性有机污染物催化氧化过程研究[D]. 北京. 中国科学院生态环境研究中心,2019.
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