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含钴锰基水滑石衍生复合氧化物的制备及其催化氧化VOCs性能研究
莫胜鹏
学位类型硕士
导师陈运法 ; 李双德
2017-07
学位授予单位中国科学院研究生院
学位授予地点北京
学位专业材料学
关键词水滑石 复合氧化物 整体式薄膜催化剂 催化氧化 Vocs
摘要

全国环境污染形势越来越严重,解决环境问题迫在眉睫。挥发性有机化合物(Volatile organic compounds,VOCs)作为大气污染物之一,不仅破坏生态环境,而且影响了人们的健康。催化氧化技术是解决空气VOCs污染问题最有效途径之一,且不会产生二次污染物,其关键问题是研制低成本、高效、稳定性好的催化剂。水滑石(Layered Double Hydroxides,LDHs)衍生得到的复合氧化物具有多孔性、高比表面积、协同效应、酸碱双功能性及晶粒高度分散等特性,在环境催化领域表现出良好的应用潜力,是制备催化反应器的主要功能组件,尤其是整体式薄膜材料。本论文旨在通过制备含Co/Mn的LDHs衍生得到多元复合氧化物催化剂,详细研究了其形貌、表面结构和化学性质,揭示了催化剂结构与催化氧化性能之间的关系;最终通过原位生长法制备ab面垂直于基底整体式薄膜催化剂。具体研究内容和结果如下:(1)Co-Al复合氧化物的结构调控及其催化氧化VOCs性能通过简单地控制反应溶剂(水、甲醇和乙醇)和氨释放剂(氨水、六次甲基四胺和尿素)合成了不同形貌的Co-Al LDHs,包括弯曲片、不完整六边形片和绒球状,比较了其氧化物对典型VOCs(苯)催化氧化性能。结果表明,采用乙醇和尿素的条件所得的绒球状的CoAl氧化物催化性能最好,在230°C下苯的转化率为99%。(2)氧化物结构缺陷及其催化氧化VOCs性能在纯氧气气氛下,将Co2+(3d7)氧化为Co3+(3d6)成功制备了CoIICoIII LDHs,煅烧后得到缺陷结构氧化物。通过激光拉曼光谱、H2-TPR、TPD和XPS表征氧化物结构缺陷(酸性位点、氧缺陷和表面价态分布),并与Co-Al氧化物比较对苯和甲苯的催化性能。原位氧化法制备的氧化物催化氧化苯、甲苯完全转化的温度分别为210°C和220°C,具有丰富的结构缺陷,诱导产生良好的低温还原性、表面路易斯酸性位点和活性氧(Oads)。(3)复合组分协同效应与催化氧化性能关系通过分别引入Co、Ce掺杂Mn-Al LDHs成功制备了三元的LDHs,经煅烧形成一系列层状复合氧化物。研究表明,LDHs主层板的金属元素种类和比例影响了复合氧化物晶型结构、比表面积、还原能力和表面物种分布,并进一步探讨煅烧温度对结构的影响。在Co-Mn-Al催化剂体系中,当Co:Mn=1:2时,比表面积最大为128.04m2 g-1,孔径分布更集中,晶粒最小,催化氧化苯转化90%的温度(T90)为238°C;在低温条件下(350°C)煅烧得到的氧化物结构更完整、比表面积高,但在高温条件下(550°C)得到的氧化物催化性能最好(T90=208°C),组分协同效应增强。在Ce-Mn-Al氧化物催化剂体系中,Ce元素掺杂Mn-Al形成固溶体促进了CeO2和MnOx的协同效应、增大Mn4+/Mn3+和晶格氧(Olatt)比例,进一步促进催化氧化苯性能。(4)整体式薄膜催化剂催化氧化VOCs性能研究基于上述研究结果,采用原位生长技术在铝箔上制备出一系列垂直生长的Co-Mn-Al LDHs,并以此为前驱体制备了整体式Co-Mn-Al氧化物薄膜催化剂,考察了对苯的催化氧化性能。研究结果表明,整体式Co-Mn-Al薄膜催化剂的最优样品催化氧化苯的T90为240°C,比二元的Mn-Al和Co-Al薄膜催化剂的T90分别降低了25°C和60°C。整体式薄膜的结构比粉体更复杂,单位质量的反应速率明显优于最优的粉体催化剂,整体式薄膜的Oads/Olatt约为0.916,而粉体的Oads/Olatt约为0.55。金属基整体式催化剂成功应用于催化VOCs,为催化反应器的制备奠定了一定实践基础。 

其他摘要

The situation of environmental pollution is more and more serious, solving environmental problems is imminent. Volatile organic compounds (VOCs) are one of the main air pollutants,which are not only harmful to the environment but also hazardous to human health. Catalytic oxidation is regarded as one of the high-efficiency way for VOCs degradation and less harmful reaction by-products. The key issue is the availability of a low-cost and stabilized catalyst with high activity in catalytic oxidation technology. The mixed metal oxides (MMO) derived from hydrotalcite-like offer a number of advantages such as pore structure, high specific surface area, synergistic effect, acid-alkali double function and grain high dispersion, which exhibit a favorable potential application in environmental field and are the components of the main function of the catalytic reactor, especially monolithic membrane materials.In this thesis, The multi-mixed metal oxides catalysts obtained by calcination of layered double hydroxides containing Co/Mn to explore the different morphology, structure, chemical properties. The relationship between the structure and catalytic performances of the catalysts was revealed. Meanwhile, the monolithic film catalysts with the ab plane in a perpendicular orientation to the substrate, were prepared with the in-situ growth method on a pure metal substrate. The main contents and results are as follows:(1)Synthesis of Co-Al composite oxides and their catalytic performances for total VOCs oxidationThe synthesis of Co-Al LDHs with different morphology nanostructures was constructed by simply controlling reaction solvents (water, methanol and ethanol) and ammonia release agents (ammonia, methenamine and urea), including frizzy platelets, imperfect hexagonal platelets and coral-like. The catalytic performances for total VOCs oxidation over all oxides were investigated. The results indicated that the coral-like Co-Al catalyst obtained under ehtanol and urea displayed the highest catalytic activity (T99 = 230°C) for benzene combustion.(2)Structure defects of composite oxides and their catalytic performances for total VOCs oxidationThe CoIICoIII LDHs with mixed valence states were prepared by the oxidation of Co2+(3d7) to Co3+(3d6) under a dynamic oxygen atmosphere. The structure defects of the samples including surface acid sites, oxygen vacancy, low-temperature reducibility and surface elemental compositions, are characterized by numerous analytical techniques, such as Raman spectroscopy, H2-TPR, TPD and XPS. It is concluded that the catalyst prepared by in-situ oxidation method displayed the higher catalytic activity (T99(benzene) = 210°C and T99(toluene) = 220°C), for which possessed the most rich surface Co3+ inducing excellent low-temperature reducibility, surface Lewis acid sites and surface active oxygen species (Oads).(3)Synergistic effects of composite components and catalytic performances relationshipA series of ternary LDHs were fabricated with the method of the Co and Ce substitution in the brucite layer of MnAl LDHs, respectively, which were completely transformed to oxide phases after calcination in air. The results indicated that the metal species and ratio of LDHs had a influence on the crystal structure, specific surface area, low-temperature reducibility, surface elemental compositions of the composite oxides. The influence of calcined temperature on the structure of composite oxides catalysts were studied. Among the Co-Mn-Al oxides, when the mole ratio of Mn/Co is 2.0, the obtained sample exhibited the highest surface area (128.04m2 g-1), the narrowest average pore size distributions and the smallest grain size of crystallites, which displayed superior catalytic activity with T90 at 238°C. Among CeMnAl samples, the replacement of Mn by Ce in the brucite layer of Mn-Al LDHs should cause the formation of a solid solution, which can obviously improve the catalytic activities due to the synergistic effects between CeO2 and MnOx, the abundant Mn4+/Mn3+ ratios and surface lattice oxygen (Olatt).(4)The catalytic performances of the monolithic film catalysts for total VOCs oxidationBased on the results mentioned above, the CoMnAl LDHs film with the ab plane in a perpendicular orientation to the substrate, was prepared with the in-situ growth method on a pure Al substrate, which was used as the precursors for fabricating the monolithic film catalysts. The catalytic performances of the monolithic film catalysts for total VOCs oxidation were investigated. It is concluded that the optimal catalyst of the monolithic CoMnAlO film catalysts exhibited the higher catalytic performance with T90 about 240°C, which were 25°C and 60°C lower than those of the binary Mn-Al and Co-Al film, respectively. The structure of the monolithic catalysts was more complicared than that of powder samples, and the monolithic catalysts exhibited a higer reaction rate, because the Oads/Olatt molar ratio of monolithic catalyst (0.916) is higher than that of powder sample (0.55). The monolithic film catalyst exhibited high catalytic efficiency in total oxidation of VOCs, which provides great potential for their practical application. 

语种中文
文献类型学位论文
条目标识符http://ir.ipe.ac.cn/handle/122111/24207
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莫胜鹏. 含钴锰基水滑石衍生复合氧化物的制备及其催化氧化VOCs性能研究[D]. 北京. 中国科学院研究生院,2017.
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