具有核壳和空心球结构的铈基催化剂的制备及其催化氧化乙苯性能的研究

发布时间：2018-06-25 04:24

  本文选题：CeO_2 + 过渡金属掺杂　； 参考：《湖南大学》2016年硕士论文

【摘要】：氧化铈作为一种环境友好和含量丰富的稀土金属氧化物,由于其本身固有的储存和释放氧特性而被广泛应用到环境和能源等领域。在各种应用中,氧化铈不仅可以作为活性组分,而且还能作为其他活性组分的良好载体。但是,氧化铈纳米颗粒热稳定性差且易团聚降低活性。采取特殊的方法将其制备成核壳结构或空心球结构不仅提高氧化铈纳米颗粒的分散度和比表面积,而且作为载体与其他材料相结合后可以增强催化剂的活性和稳定性。单羧基钴卟啉作为仿生均相催化剂在催化氧化反应中表现出良好的活性,但是其易自聚、难回收等缺点限制了它的应用。解决这个问题的一种方法是,将钴卟啉负载到无机载体上制备出非均相催化剂。该非均相催化剂通过载体提供的微环境可大大提高其稳定性和抗氧化能力。另一种方法是将钴卟啉在惰性气氛中热解合成新型Co-N-C材料来提高卟啉的原子利用率。综上所述,本文合成了几种新型负载催化剂,以氧气作为绿色氧化剂,在无溶剂条件下通过催化氧化乙苯来考察其催化性能。具体的研究内容如下：1.通过改进的Stober法和表面活性剂作用制备以过渡金属掺杂氧化铈为核二氧化硅为壳的核壳结构载体,然后将经过APTES改性的钴卟啉以化学键键联到载体上,得到一系列表面负载钴卟啉的二氧化硅@双金属氧化物催化剂(CoTPP-SiO2@(MOx/CeO2) (M=Fe、Co、Mn和Cu))。以乙苯氧化反应为探针反应考察不同过渡金属掺杂氧化铈晶格所得的催化剂催化氧化乙苯反应的催化性能及其稳定性,结果显示钴金属掺杂的催化剂(CoTPP-SiO2@(CoOx/CeO2))催化活性最好,乙苯转化率为28.5%,苯乙酮选择性为76.8%。2.以单羧基钴卟啉为Co-N-C材料的前驱体,在氮气氛下,500℃热解CoTPP-SiO2@(CoOx/CeO2)核壳材料,得到Co-N-C/SiO2@(CoOx/CeO2)催化剂。结果显示,催化剂热解后出现Co-Nx结构,这有利于提高催化剂的活性和稳定性。该催化剂循环催化氧化乙苯反应6次之后,其活性损失明显比热解前催化剂(CoTPP-(CoOx/CeO2)活性损失小很多。单羧基钴卟啉热解得到的Co-N-C很大程度上提高了催化剂的稳定性。3.采用层层包裹的策略,以SiO2微球为硬模板制备(MnOx/CeO2)@SiO2核壳结构,然后将改性的钴卟啉化学键联到表面,再在外面包裹一层SiO2,在氮气氛下500℃焙烧处理1h后,最后用氢氧化钠刻蚀得到Co-N-C负载在空心球MnOx/CeO2上的催化剂。该催化剂中的Co-N-C是嵌入在载体孔隙中的,提供了“纳米反应器”环境。具有高比表面积、大孔腔等特性的催化剂在乙苯氧化反应方面表现出优异的性能,乙苯转化率达到44.5%。并依据文献和特设的实验考察了催化剂催化氧化乙苯的机理。结果显示,Co-N-C/(MnOx/CeO2)空心球由于氧空穴造成的表面活性氧和Co-Nx结构是其主要的活性位。
[Abstract]:As an environmentally friendly and rich rare earth metal oxide, cerium oxide has been widely used in environmental and energy fields due to its inherent storage and oxygen release properties. In various applications, cerium oxide can be used not only as active component, but also as a good carrier of other active components. However, the thermal stability of cerium oxide nanoparticles is poor and the agglomeration is easy to reduce the activity. The core-shell structure or hollow sphere structure can not only improve the dispersion and specific surface area of cerium oxide nanoparticles, but also enhance the activity and stability of the catalyst when the support is combined with other materials. Monocarboxylic cobalt porphyrins show good activity in catalytic oxidation as bionic homogeneous catalysts, but their easy self-polymerization and difficult recovery limit their application. One way to solve this problem is to prepare heterogeneous catalysts by loading cobalt porphyrin onto inorganic support. The stability and oxidation resistance of the heterogeneous catalyst can be greatly improved by the microenvironment provided by the support. Another method is to pyrolyse cobalt porphyrin in inert atmosphere to synthesize a new Co-N-C material to improve the atomic utilization ratio of porphyrin. To sum up, several novel supported catalysts were synthesized and their catalytic properties were investigated by catalytic oxidation of ethylbenzene under solvent-free conditions with oxygen as green oxidant. The specific contents of the study are as follows: 1: 1. The core-shell structure carrier with transition metal-doped cerium oxide as the core silica shell was prepared by the modified Stober method and the surfactant interaction. Then the cobalt porphyrin modified by APTES was chemically bonded onto the carrier. A series of surface supported cobalt porphyrin supported silica @ bimetallic oxide catalysts (CoTPP-SiO2 @ (MOX / CEO _ 2) (mn and Cu).) were prepared. The catalytic performance and stability of catalysts obtained from different transition metal doped cerium oxide lattices for the oxidation of ethylbenzene were investigated using ethylbenzene oxidation reaction as probe reaction. The results showed that cobalt doped catalysts (CoTPP-SiO2 @ (CoOxp / CeO2) had the best catalytic activity. The conversion rate of ethylbenzene was 28.5.The selectivity of acetophenone was 76.80.2. Co-N-C / SiO2@ (CoOxp-CeO2) core-shell materials were pyrolyzed at 500 鈩，

本文编号：2064558