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二氧化锰分级结构的调控合成及其苯催化氧化性能研究
Alternative TitleControllable Synthesis of Hierarchical Manganese Oxide and Application in Abatement of Benzene
李东艳
Subtype博士
Thesis Advisor陈运法
2013-05-01
Degree Grantor中国科学院研究生院
Degree Discipline化学工程
Keyword二氧化锰   中空结构   水热法   催化氧化   苯
Abstract锰的自然资源相对丰富,价格低廉,无毒对环境友好。锰有多种可变的价态,以致电子很容易发生转移,所以氧化锰化合物具有很高的电化学性能和良好的催化活性。二氧化锰的结构较复杂,晶型繁多,在化学组成上一般还含有低价锰离子和OH-,而且有些还含有K、Na等金属离子,至今尚未完全研究透彻。二氧化锰在去除挥发性有机化合物中表现出了优异的性能,但其去除苯的研究还较少。二氧化锰的物理化学性质与晶型和形貌有着密切的联系,为此本文制备了不同晶型和形貌的二氧化锰,并考察它们对苯的催化氧化性能,寻求其相互关系与影响规律。(1) 以硫酸锰、过硫酸钾和盐酸为原料,采用水热方法,通过无模板自组装过程制备了由均一尺度的纳米棒组成的分级中空β–MnO2微球,考察了反应条件对产物形貌和晶型的影响。通过调控反应条件制备了分级双壁结构的β–MnO2/α–MnO2和由纳米棒及纳米线共同组成的分级中空α–MnO2,提出了分级中空微球的形成机理,同时考察了空心微球和纳米棒对苯的催化氧化效果。结果表明,由纳米线和纳米棒组成α–MnO2中空微球对苯催化氧化性能最好。(2) 以高锰酸钾和盐酸为原料,采用水热方法,通过改变反应时间、反应温度以及原料的浓度等条件分别制备了由纳米管组成的中空微球、多脚纳米管、由纳米片和纳米线共同组成的微球。并提出纳米管组成的分级中空微球的形成机理,实验结果表明盐酸的用量对产物的形貌和晶型有显著的影响。在一定范围内调控反应条件可以得到分级中空微球。同时考查了不同形貌的α–MnO2对苯的催化氧化效果。分析结果表明,由纳米片和纳米棒组成的微球对苯的催化氧化效果最好。(3) 以高锰酸钾和硝酸为原料,通过在反应系统加入Ce离子,利用水热方法制备了由纳米片和纳米棒共同组成的分级中空微球。Ce均匀地掺杂进入二氧化锰的结构中,Ce离子对纳米片和纳米棒共同组成的中空微球的形成起着关键的作用。Ce离子的存在使反应系统中的电势增加,同时在Ostwald作用下形成分级中空微球。不同形貌的样品对苯的催化氧化测试结果表明:Ce的存在可以提高催化性能,Ce3+所占比例大有利于催化性能的提高。(4) 以硫酸锰、高锰酸钾为原料在硝酸环境下,采用可以简单大量制备催化剂的回流法,在50 ℃下制备了比表面积为259.4 cm2/g、由纳米棒组成的分级微球。分级微球的催化效果优于90 ℃下制备的纳米棒分子筛。通过改变实验条件,在室温下制备得到了与50 ℃回流法得到的样品的催化效果接近的催化剂。进而以室温下制备的高比表面二氧化锰为载体,制备Pt负载催化剂。结果表明2 %负载量的催化剂的催化效果最好,在约135 ℃时达到了50 %的转化,在约160 ℃时达到了90 %的转化,在200 ℃达到了接近100 %的转化。
Other AbstractManganese is low cost, environmental friendly and abundant in nature. Manganese oxide exhibits high electrochemical performance and good catalytic activity due to its variable oxidation states which lead to the electrons can easily transfer in the structure. However, a complete understanding of manganese oxide is still out of the knowledge because of its many various polymorphs and possible existence of the foreign cations such as H2O or metal ions. Manganese dioxides exhibit excellent performance in removal of volatile organic compounds. However, the research of the application of manganese dioxides in the removal of benzene is not enough. The physicochemical properties of manganese dioxide depend on its morphology and crystalline structure. In this paper, manganese dioxides with different morphology and crystalline structure were synthesized and the catalytic abilities for the oxidation of benzene were investigated.(1) Three type hierarchical MnO2 microspheres, viz., hierarchical hollow β-MnO2, hierarchical hollow α–MnO2 and hierarchical double-walled β–MnO2/α–MnO2, have been synthesized by a facile hydrothermal method without employing any templates, catalysts, surfactants or calcinations. The possible formation mechanism of hierarchical hollow microspheres is proposed. The catalytic abilities for the oxidation of benzene are investigated. The hierarchical hollow α–MnO2 assembled by nanorods and nanowires exhibits the best catalytic abilities among the samples. (2) Hierarchical hollow α-MnO2 microspheres assemled by nanotubes and nanorods, multipods nanotube, microspheres composed by nanorods and nanosheets were controllable synthesized by a facile hydrothermal method based on a direct reaction between KMnO4 and HCl. The concentration of HCl plays a crucial role in controlling the morphology and crystalline structure of MnO2. The possible formation mechanism of hierarchical hollow microspheres assembled by nanotubes is proposed. The catalytic abilities for the oxidation of benzene of the samples with different morphology are investigated. The results indicated that the microshpheres assembled by nanorods and nanosheets are the best catalyst among the tested samples.(3) Hierarchical hollow MnO2 microspheres consisted of “discus-like” nanoplatelets and nanorods have been synthesized by a facile hydrothermal method based on the decomposition of KMnO4 precursor in nitric acid solution in the presence of Ce3+ ions. Cerium uniformly distributes in the sample. The concentration of Ce3+ ions is a key factor for the formation of the hierarchical hollow microspheres. The presence of the Ce3+ ions increases the ionic strength of the reaction system. The oriented attachment and subsequent Ostwald ripening process are responsible for the formation of the hierarchical hollow structures. More Ce3+ inos lead to more amounts of defective oxides or surface adsorbed oxygen, which enhance the mobility of lattice oxygen on the surface to be activated. (4) The hierarchical urchin manganese oxide microspheres were synthesized via a facile method based on the reaction between KMnO4 and MnSO4 in nitric acid solution at 50 °C. The Brunauer–Emmet–Teller (BET) surface area of the urchin microspheres is 259.4 cm2/g. The catalytic ability for the oxidation of benzene of the hierarchical urchin is better than that of nanorod OMS. Meanwhile, the sample with nearly same catalytic ability for the oxidation of benzene was prepared at room temperature. Pt–MnO2 was prepared with the MnO2 obtained at room temperature. The catalytic abilities for the oxidation of benzene of different content Pt–MnO2 were test. The catalyst with 2% Pt is the best one among the samples. The 50% oxidation of benzene on the sample is at about 135 ℃ and the 90% oxidation of benzene is about 160 ℃. The conversion of benzene almost reaches 100 % at 200 ℃.
Pages125
Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/8241
Collection研究所(批量导入)
Recommended Citation
GB/T 7714
李东艳. 二氧化锰分级结构的调控合成及其苯催化氧化性能研究[D]. 中国科学院研究生院,2013.
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