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钯基催化剂上 1 ,2 二氯苯催化降解过程及机理研究
Alternative TitleStudy on the C atalytic D egradation Process and M echanism of 1,2 D ichlorobenzene over Pd based C atalysts
李娜
Subtype博士
Thesis Advisor郝郑平
2020-06
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催化降解 1,2 二氯苯,副产物分布,多氯有机化合物,反应机理 Catalytic DegradatIon 1,2 d Ichlorobenzene b y Products DistributIon p Olychlorinated Organic Compounds r Eact Ion Mechanism
Abstract

       含氯挥发性有机污染物对自然环境和生物健康具有严重的危害。阐明含氯挥发性有机化合物催化氧化中 有毒污染物及其形成机理,对于详细了解污染物的降解 过程 以及同时去除二次有毒 污染物至关重要。 论文 系统全面的考察了 Pd 基催化剂及不同的反应气氛对 1 2 二氯苯 1,2 DC B 催化降解过程中副产物形成 的影响,揭示 了 1 2 二氯苯的催化反应过程 及 机理。得到的主要研究 结果及规律性认识 如下:
      1.研究了 催化剂 Pd /γ Al 2 O 3 Pd/ ZSM 5 和 Pd SiO 2 对 催化氧化 1,2 DC B的影响 。在 催化氧化过程中,检测到多种多氯 有机副产物,如三氯苯,四氯苯和五氯苯。反应温度与 载体类型在形成氯化有机副产物中起着至关重要的作用。随着反应温度的升高,有机副产物的氯化度逐渐增加 。 并且在低温下,多氯代有机副产物的 总 浓度急剧增加,然后在反应温度高于 450 ºC 时 开始 降低。同时,多氯 有机副产物的 量随着 催化剂载体 硅铝比的增加而增加。 在此基础上 还 提出了多氯 有机化合物的形成机理。
      2.合成了一系列具有不同 Pd 粒径的 Pd /γ Al 2 O 3 催化剂, 研究了 Pd 的粒径大小对 1,2 DCB 催化性能的影响 。 结果表明,钯的纳米尺寸越小, 1,2 DCB 的催化活性越高 这主要与 Pd 的氧化态和表面吸附的氧有关。而且, Pd /γ Al 2 O 3 催化剂在干燥和潮湿条件下对 1,2 DCB 催化氧化 具有优异的稳定性 。 但是反应过程中仍能检测到含氯副产物生成,其浓度随 催化剂表面 Lewis 酸浓度的增加而降低,随反应温度呈现火山型变化 。 水对氯化反 应具有一定的 抑制 作用。 此外, 根据 原位 FTIR 和 UV vis DRS 表征 结果,提出了 1,2 DCB 的催化 氧化和氯化 反应都 遵循 Langmuir Hin shelwood 类型 的机理。
       3.研究了不同氧气及水蒸气浓度对 Pd/ ZSM 5 25) 催化剂上 1,2 DCB 的催化降解 过程 的影响 。发现降低氧气 浓度 和 反应气氛中添加水蒸气不仅能够提高催化反应活性还能够降低反应过程中含氯有机副产物的形成 ,主要是由于其 可以抑制 氯化反应 过程中氯化剂 氯化的钯物种的形成 。 此外, 1 ,2 DCB 在 Pd/ZSM 5( 25)催化剂上,水作为唯 一氧化剂(水解氧化)的情况下也行实现完全催化降解;且反应过程中只检测到苯、氯苯和1, 3 二氯苯。 在催化氧化和水解氧化过程中形成了相似的表面物种,因此 1,2 DCB 的 催化氧化和水解氧化 具有 相似 的 催化降解反应 机理。
        4.研究了 Pd /γ Al 2 O 3 Pd/ ZSM 5 和 Pd SiO 2 催化剂 对 1,2 DCB 水解氧化的影响 。 Pd/ ZSM 5 25) 催化剂 表现 出最佳的水解氧化活性 。主要是由于Pd/ ZSM 5 25) 催化剂具有较窄的 孔道和较高的铝含量 ,这有助于形成质子化的水分子。这种水分子可以加速碳和氯的去除,从而使 P d/ ZSM 5 25) 催化剂具有很高的活性。但是, HCl 的形成会导致 Pd/ ZSM 5 25) 催化剂的脱铝 进而导致 骨架的 坍塌 ,从而导致 Pd/ ZSM 5 25) 催化剂在水解氧化反应中的稳定性较差。

Other Abstract

      Chlorine d Volatile organic compounds (VOCs) are harmful to the natural environment and biological health. Cl arifying the oxidative products and their formation mechanisms in the catalytic oxidation of chlorinated volatile organic compounds is important to provide detailed understanding of the degradation of pollutants with the simultaneous removal of secondary p ollutants. In this paper , the effects of P d based catalysts and different reaction atmosphere on the formation of organic by products during 1,2 dichlorobenzene (1,2 DCB) catalytic degradation were systematically investigated, and the catalytic reaction pr ocess and mechanism of 1,2 dichlorobenzene were revealed. The main research results and regularity are as follows:
      1.The effect of catalysts (Pd/ γ Al 2 O 3 , Pd/ZSM 5, and Pd/SiO 2 on catalytic oxidation of 1,2 dichlorobenzene (1,2 DCB) was investigated . Durin g the oxidation processes, a variety of polychlorinated organic by products, such as trichlorobenzene,tetrachlorobenzene and pentachlorobenzene were detected. The reaction temperature and types of supports played a vital role in the formation of chlorina ted organic by products With an increase of in the reaction temperature, the degree of chlorination of the organic by products increase d gradually , and the concentration of polychlorinated organic by products was increased sharply at low temperature s and then began to decrease when the reaction temperature was above 450 ºC. Meanwhile,the amounts of polychlorinated organic by products increased with an increasing silicate to aluminium ratio On this basis the formation mechanism s of the
polychlorinated or ganic compounds w ere proposed.
       2. A series of Pd /γAl2O3 catalysts with different Pd particle size were synthesized. The effect of Pd particle size on the catalytic performance of 1,2 DCB was studied. The results show that the smaller the size of palladium is, the higher the catalytic activity of 1,2 DC B is. This is mainly related to the oxidation state of Pd and the oxygen adsorbed on the surface. Moreover,P d /γ Al 2 O 3 catalyst has excellent stability for 1,2 DCB catalytic oxidation under dry and wet conditions. However, the formation of organic by produ cts can still be detected in the reaction process. The concentration of organic by products decreases with the increase of Lewis acidity, and shows volcano shaped with the reaction temperature. Water can partially restrain chlorination . Furthermore, based on the results of i n situ FTIR and UV vis DRS experiments it is proposed that the catalytic oxidation and chlorination of 1,2 DCB are following the Langmuir Hin shelwood type of mechanism.
      3. The effect of oxygen pressure and water concentration during th e catalytic degradation of 1,2 DCB over Pd/ ZSM 5 25) catalyst was studied. It was found that the reduction of oxygen pressure and the addition of water vapor in the reaction atmosphere could not only improve the catalytic activity, but also reduce the form ation of chlorinated organic by products, mainly because it could inhibit the formation of chlorinated palladium species. In addition, 1,2 DCB can be completely degraded on Pd ZSM 5(25) catalyst with water as the only oxidant (hydrolytic oxidation), and on ly benzene, chlorobenzene and 1,3 d ichlorobenzene can be detected.Similar surface species were formed in the process of catalytic oxidation and hydrolytic oxidation, so the catalytic oxidation and hydrolytic oxidation of 1,2 DCB have similar mechanism of catalytic degradation.
      4. The effects of Pd/ γ Al 2 O 3 , Pd/ZSM 5, and Pd/SiO 2 catalysts on the 1,2 DCB hydrolysis oxidation were studied. Pd/ ZSM 5 25) catalyst showed the best hydrolysis oxidation activity. The main reason is that Pd/ ZSM 5 25) catalyst has narrow pore and high aluminum content, which i s helpful to form protonated water molecules. This kind of water molecule can accelerate the removal of carbon and chlorine, so Pd/ ZSM 5 25) catalyst has high activity. However, the formation of HCl will lead to the dealumination of Pd/ ZSM 5 25) catalyst a nd then the collapse of the framework, resulting in the poor stability of Pd/ ZSM 5 25) catalyst in the hydrolysis oxidation reaction.

Pages166
Document Type学位论文
Identifierhttp://ir.rcees.ac.cn/handle/311016/43621
Collection环境纳米技术与健康效应重点实验室
Recommended Citation
GB/T 7714
李娜. 钯基催化剂上 1 ,2 二氯苯催化降解过程及机理研究[D]. 北京. 中国科学院生态环境研究中心,2020.
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