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分子筛催化材料上乙烯低温完全氧化和部分氧化反应研究
Alternative TitleStudies on Low-Temperature Complete Oxidation and Partial Oxidation of Ethylene over Zeolite-Based Catalysts
杨洪玲
Subtype博士
Thesis Advisor郝郑平
2018-06
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乙烯,低温氧化,环氧乙烷,分子筛,反应机理 Ethylene, Low-temperature Oxidation, Ethylene Oxide, Zeolite, Reaction Mechanism
Abstract

      传统的催化体系在乙烯完全氧化反应中温度高、催化性能差、制备复杂,在乙烯部分氧化制备环氧乙烷反应中也存在温度高、活性低、选择性差等问题,对催化体系进行优化以实现降低反应温度、提高催化稳定性和选择性,可以从源头上实现节约能耗和降低污染的目的。本论文主要针对乙烯低温完全氧化消除和部分氧化制备环氧乙烷反应,分别建立了微孔分子筛催化体系和锰分子筛催化体系,系统考察了催化剂的催化性能,结合多种技术手段深入分析了催化剂的结构特征、表面特性及影响催化剂性能的主要因素,揭示乙烯完全氧化和部分氧化的催化反应过程和催化反应机理。得到的主要结论如下:

      (1)Ag/分子筛催化材料上乙烯低温完全氧化反应

       研究不同骨架结构类型的微孔分子筛(ZSM-5、Beta、Y和Mordenite)负载银上乙烯的完全氧化性能。在25oC干湿条件下可实现100 ppm乙烯的完全催化氧化。研究发现,分子筛的骨架类型和相对湿度影响其催化稳定性,微孔分子筛的布朗斯特(Br?nsted)酸对其催化活性有非常重要的影响。相比于其它负载型催化剂,Ag/ZSM-5因具有较丰富的Br?nsted酸位点,因此表现出最好的催化稳定性。吸附在Br?nsted酸位上的水导致可利用的Br?nsted酸量的减少,从而使得Ag/分子筛催化剂的活性降低。

      (2)Ag/ZSM-5催化材料上乙烯低温完全氧化反应

       制备了系列不同硅铝比的微孔ZSM-5负载银催化剂用于乙烯的完全氧化反应。所有的Ag/ZSM-5催化剂在室温下可100%完全氧化乙烯。ZSM-5的硅铝比是决定Ag/ZSM-5催化剂稳定性的重要因素。硅铝比为38的ZSM-5负载银催化剂在25oC条件下100%的初始活性可保持接近7小时,主要归因于其具有较丰富的Br?nsted酸位点,其可以为乙烯的氧化提供活性位。机理研究表明,Ag/ZSM-5催化剂失活的主要原因是水和乙烯在Br?nsted酸位点上的竞争吸附,水优先吸附在Br?nsted酸位点上形成水合Br?nsted酸。水的吸脱附动力学表明,对于硅铝比为38的ZSM-5负载银催化剂来说,相对较慢的吸附水速率和相对较快的脱附水速率有利于提高其催化稳定性。

      (3)氟改性的Pt/ZSM-5催化材料上乙烯低温完全氧化反应

      研究发现微孔Pt/ZSM-5催化剂在乙烯低温完全氧化反应中表现出优异的催化性能,经氟(F)改性的Pt/ZSM-5催化剂进一步提高了其催化稳定性。0.5%Pt/F-ZSM-5在25oC条件下100%的乙烯转化率可维持11小时以上。研究表明,微孔分子筛催化剂的酸性和耐水性是影响催化剂稳定性的关键因素。对ZSM-5进行氟化处理,一方面,由于F的诱导作用提高了催化剂的Br?nsted酸性,有利于乙烯分子在催化剂上吸附和活化,同时,氟化处理后提高了催化剂的耐水性,从而延长了催化剂的寿命。

      (4)Ag/Al-氧化锰八面体分子筛催化材料上乙烯低温部分氧化反应

       研究了铝掺杂的氧化锰八面体分子筛负载银上乙烯的部分氧化性能。发现氧化锰八面体分子筛负载银催化体系在乙烯低温部分氧化反应中表现出较好的催化活性、较高的环氧乙烷(EO)选择性和产率。将Al引入到Ag/氧化锰八面体分子筛催化剂显著地提高了催化剂的活性和EO选择性。在90oC时,EO产率可达10%,在150oC时,EO产率可达43.5%,远高于工业催化剂Ag/Al2O3。Al的引入增加了催化剂晶格氧的浓度、提高了活性氧的流动性,从而提高了反应活性。

Other Abstract

       The traditional catalyst systems have high reaction temperature, complicated preparations and poor catalytic performance for the complete oxidation of ethylene, and also exist the shortcomings of high reaction temperature, low activity and poor selectivity in ethylene epoxidation reaction. Opitimizing those catalyst systems could reduce reaction temperature, improve catalytic stability and selectivity, and so as to achieve the objective of energy saving and emission reduction from the sources.

      In this thesis work, environmental friendly microporous zeolite catalysts and manganese oxide octahedral molecular sieve catalysts were applied in the complete oxidation of ethylene and epoxidation of ethylene, respectively, and investigated the catalytic performance. The structural and surface properties of catalyst, and the main factors affecting the catalyst performance were extensively characterized and elucidated by using various technologies, the reaction processes and mechanisms of ethylene complete oxidation and epoxidation were thoroughly discussed. The main research results are listed as follows:

      (1) Low-temperature complete oxidation of ethylene over Ag/zeolite catalysts

      Microporous zeolite (ZSM-5, Beta, Y and Mordenite) supported silver catalysts were studied for the complete oxidation of ethylene, achieving 100% of 100 ppm of ethylene mineralized into CO2 at 25oC in both dry and humid atmosphere. It is found that the Br?nsted acid sites of microporous zeolite play an important role in ethylene oxidation. Moreover, the zeolite framework type and relative humidity have a significant effect on catalytic stability. Ag/ZSM-5 exhibits the highest catalytic stability due to the larger number of Br?nsted acid sites. The adsorbed H2O onto Br?nsted acid sites leads to the disappearance of available Br?nsted acid sites, and thus results in the activity loss of Ag/zeolite catalysts.

      (2) Low-temperature complete oxidation of ethylene over Ag/ZSM-5 catalysts

       Microporous Ag/ZSM-5 catalysts with different SiO2/Al2O3 ratios were prepared and evaluated for ethylene oxidation. Ethylene can be completely oxidized into CO2 by all Ag/ZSM-5 catalysts at 25oC. It is found that SiO2/Al2O3 ratio of ZSM-5 has a significant effect on catalytic stability. Ag/ZSM-5 with SiO2/Al2O3 ratio of 38 exhibits enhanced catalytic stability compared with other Ag/ZSM-5 catalysts. The 100% conversion of ethylene over Ag/ZSM-5 with SiO2/Al2O3 ratio of 38 can be maintained for nearly 7 h, due to its larger number of Br?nsted acid sites, as Br?nsted acid sites can provide active sites for ethylene oxidation. The mechanism research indicates that the main reason for Ag/ZSM-5 catalyst deactivation is the competitive adsorption of ethylene and water vapor on Br?nsted acid sites, water vapor preferentially adsorbs on Br?nsted acid sites to form hydrous Br?nsted acid. Water vapor adsorption-desorption kinetics results demonstrate that slow adsorption and fast desorption characters of water vapor on Ag/ZSM-5 with SiO2/Al2O3 ratio of 38 contribute to its good catalytic stability for ethylene oxidation.

      (3) Low-temperature complete oxidation of ethylene over fluorine modified Pt/ZSM-5 catalysts

      The microporous Pt/ZSM-5 catalyst prepared in this study revealed excellent catalytic performance in ethylene oxidation. The modification of fluorine (F) on Pt/ZSM-5 efficiently improves the catalyst stability. The conversion of ethylene over 0.5%Pt/F-ZSM-5 can sustain at 100% for more than 11 h at 25oC. This study shows that the acidity and water tolerance of catalysts are crucial factors affecting the catalytic stability. The enhancement of Br?nsted acidity of the F-treated ZSM-5 is favorable for the adsorption and activation of ethylene molecules onto the Pt/F-ZSM-5 catalysts. The F-modification prolongs the catalyst life by improving its water tolerance.

      (4) Low-temperature epoxidation of ethylene over aluminum doped-manganese octahedral molecular sieves supported silver catalysts

      The Al doped-manganese octahedral molecular sieves supported silver (Ag/Al-OMS-2) catalysts were prepared and evaluated for ethylene epoxidation reaction. It is found that Ag/OMS-2 shows high catalytic activity, high ethylene oxide (EO) selectivity and yield in low-temperature epoxidation of ethylene. The incorporation of Al into Ag/OMS-2 catalyst significantly improves the catalyst activity and EO yield. At 90oC, the yield of EO can reach 10%, and at 150oC, the yield of EO can reach 43.5%, which are much higher than the commercial catalyst Ag/Al2O3. The incorporation of Al increases the lattice oxygen content and the active oxygen species mobility, thus enhances the reaction activity.

Pages169
Language中文
Document Type学位论文
Identifierhttp://ir.rcees.ac.cn/handle/311016/41565
Collection环境纳米技术与健康效应重点实验室
Recommended Citation
GB/T 7714
杨洪玲. 分子筛催化材料上乙烯低温完全氧化和部分氧化反应研究[D]. 北京. 中国科学院生态环境研究中心,2018.
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