【作者】 刘媛；

【导师】 刘昌俊；

【作者基本信息】 天津大学 ， 化学工艺， 2010， 博士

【摘要】 微孔和介孔分子筛由于具有规则的孔结构、大的比表面积、高的孔隙率、可调控的孔分布、独特的择形选择性、固体酸性、离子交换性等特点而广泛地应用于化学工业中,通常被用作载体、吸附剂、催化剂等。随着新能源技术和环境技术等的发展,微孔和介孔分子筛的应用将会越来越广泛。通常分子筛材料的合成需要引入有机模板剂,又称结构导向剂。有机模板剂对于分子筛骨架结构的形成起着至关重要的作用。但是,刚刚合成的分子筛,模板剂分子往往存在于孔道或者笼中,只有模板剂被脱除以后,分子筛的孔道才能开放。目前,最常用的脱除模板剂的方法是热焙烧方法。这种方法通常需要严格控制操作条件,如温度、升温速率、气氛等。尽管热焙烧方法可以有效地脱除模板剂,但是可能会引起分子筛骨架结构的破坏或收缩,因此,开发一种低温、高效、便捷的模板剂脱除方法意义重大。本文采用室温下启动、大气压下操作、以空气或氧气为等离子体发生气的介质阻挡放电等离子体方法来脱除ZSM-5、Hβ、MCM-41分子筛以及氧化锆(C77Zr)样品的模板剂。实验结果表明,介质阻挡放电等离子体可以有效地脱除ZSM-5、Hβ、MCM-41分子筛以及C77Zr样品的模板剂。与热焙烧方法相比,介质阻挡放电方法脱模板剂的速率提高了大约8倍。在脱除模板剂过程中,介质阻挡放电等离子体的热效应并不明显。介质阻挡放电方法制备的样品骨架收缩程度也比热焙烧方法小。吡啶吸附的红外光谱结果表明,介质阻挡放电等离子体可以增加分子筛表面Br?nsted酸和Lewis酸位。另外,介质阻挡放电等离子体脱模板剂过程中不使用任何化学试剂。因此,可以说,介质阻挡放电方法是一种快速的、方便的、环境友好的脱除分子筛模板剂的方法。在使用介质阻挡放电等离子体脱除MCM-41分子筛模板剂的过程中,观察到了具有靶波特征的等离子体斑图。之后,又在SBA-15和SiO2粉末存在下也观察到了类似的斑图现象,这是首次观察到在大气压环境下粉末形成的斑图。它可以为等离子体的相关学科提供便于操作的实验方法或模型。氧原子以及臭氧等强氧化性物质对模板剂的脱除起主要作用,而高能电子的轰击也会使模板剂分子分解。C77Zr样品上的活性炭模板剂也可以通过氧气介质阻挡放电等离子体脱除,这也证明,氧化作用是介质阻挡放电方法脱除模板剂的主要因素。为了证明介质阻挡放电方法脱除模板剂的有效性,以脱除模板剂后的MCM-41分子筛作为载体制备了Pd/MCM-41催化剂,并成功用于Suzuki反应,获得了很好的催化活性。实验还采用介质阻挡放电等离子体方法在脱除分子筛模板剂的同时分解负载在上面的PdCl2,制备了PdO/HZSM-5催化剂,用于甲烷催化燃烧反应,发现等离子体一步法制备的催化剂催化活性很好。因此,介质阻挡放电等离子体可以在脱除分子筛模板剂的同时分解催化剂前驱体用来一步法制备催化剂,由此简单、快速、高效地制备催化剂。更多还原

【Abstract】 Microporous and mesoporous molecular sieves possess uniform pore structure, large surface area, high porosity, controllable and narrowly distributed pore sizes, unique shape selectivity, solid acidity, and ion exchangeability. These materials can be applied as supports, adsorbents and catalysts in the chemical industry. With the development of new energy technology, environmental technology and many others, microporous and mesoporous materials will have more and more applications.Microporous and mesoporous molecular sieves are normally synthesized in the presence of organic templates. The template performs as a structure-directing agent that is critical for control of the frameworks. However, the template molecules remain trapped within the frameworks and have to be removed from the pores after the synthesis. At present, the most commonly method used to remove the template is the thermal calcination under strictly controlled conditions (i.e., temperature, heating rate and atmosphere type). Although the templates can be burnt off effectively, the thermal route may cause shrinkage of the frameworks. Alternatives to the conventional calcination are desired.In the present work, we attempt to remove the template from ZSM-5, Hβ, MCM-41 molecular sieves and zirconia (C77Zr) using a novel dielectric-barrier discharge (DBD) plasma technique. The DBD plasma, which is initiated at room temperature and operated at atmospheric pressure, has been successfully applied for the template removal from materials above mentioned. The template removal rate from the molecular sieves using DBD is about eight times higher than that using the conventional thermal calcination. The thermal effect is not significant during the template removal using DBD. The experiments indicated that the shrinkage of framework structure for plasma prepared sample is less than that for thermally treated sample. Upon FT-IR analyses, the DBD plasma can lead to enhanced Br?nsted acid and Lewis acid sites. In addition, there is no hazardous reagent used during the DBD template removal. According to the present results, we would suggest that the DBD plasma technique could be a fast, facile and environmental friendly alternative to the conventional thermal calcination for the template removal. In addition, during the template removal from MCM-41, the DBD plasma patterns with characteristics of target waves were observed. The similar patterns were also observed in the presence of SBA-15 and SiO2. This is the first time that the DBD plasma patterns like this were observed. It provides a convenient model for the related subjects of plasmas.The oxidation with active oxygen species like O and O3 is important for the template removal. In addition, energetic electron bombardment resulted in the decomposition of template moleculars. The removal of activated carbon template from the C77Zr sample confirmed the oxidation mechanism of the template removal using DBD plasma.In order to confirm the effectiveness of this novel plasma template removal method, the plasma prepared and thermally calcined MCM-41 samples were tested as catalyst support. Suzuki reaction was carried out over the MCM-41 supported Pd catalysts. The plasma prepared MCM-41 supported Pd catalyst shows a slightly higher yield, compared to the calcined MCM-41 supported Pd catalyst.In this work, DBD plasma has also been successfully applied for removing the template from the HZSM-5 and decomposing the PdCl2 to PdO simultaneously. Such prepared catalyst presents a higher catalytic activity over the catalyst prepared by thermal calcination in the reaction of methane combustion. The DBD plasma method is a good method for template removal and decomposition of catalyst precursor simultaneously, which represents a simple and fast method for catalyst preparation.更多还原