5-羟甲基糠醛选择性氧化反应的新型催化剂合成及性能研究

发布时间：2018-02-28 16:25

  本文关键词： 5-羟甲基糠醛 选择氧化 2 5-呋喃二甲酸 2 5-二甲酰基呋喃　出处：《华东理工大学》2017年博士论文　论文类型：学位论文

【摘要】：生物质作为一种清洁的可再生资源,可作为化石能源的替代品,是未来可持续能源系统的重要组成部分。当前研究阶段,生物质转化过程主要通过生物发酵、化学转化等方法得到一系列平台化合物,如丁二酸、5-羟甲基糠醛(5-HMF)等,然后通过催化转化合成各类高附加值化学品和燃料。其中,5-HMF氧化反应的产物2,5-呋喃二甲酸(FDCA)和2,5-二甲酰基呋喃(DFF)有重要的工业化应用价值,近几年受到广泛关注。本文针对当前5-HMF选择氧化反应研究中需引入强碱、贵金属催化剂成本高以及非贵金属催化剂活性组分利用率低的问题,分别合成了碱式碳酸锌(ZOC)负载的Au-Pd合金催化剂(Au-Pd/ZOC)、Mn-Co-O复合氧化物催化剂和改性二氧化钛(P25)负载的M_nOx催化剂(M_nOx/P25-600-5h),考察相应催化剂在5-HMF选择氧化反应中的活性,并对其物相组成、微观结构等进行详细表征,探究催化剂的微观结构与催化性能间的关联。本文的主要研究内容如下:为避免使用强碱性反应介质,通过水热法合成ZOC载体,然后采用沉积-沉淀法制备了 Au-Pd/ZOC合金催化剂,在弱碱性条件下催化5-HMF选择氧化反应可得到99%的FDCA收率。表征结果显示Au和Pd形成纳米合金粒子均匀地分散在载体ZOC上,Au和Pd之间存在的协同效应有助于提高催化活性。同时发现催化剂的活性顺序与相应载体水溶液pH值的高低顺序一致,说明载体的表面酸碱性质对催化活性有重要影响。此外,弱碱环境有利于稳定ZOC载体,提高Au-Pd/ZOC的稳定性,使其循环使用7次无明显活性降低。针对贵金属催化剂成本高的问题,采用液相混合固相煅烧法合成了 Mn-Co-O复合氧化物催化剂,其活性远高于采用相同方法制备的单一 M_nO_2和Co_3O_4。当Mn/Co摩尔比为1、锻烧温度为400℃时,所制备的Mn_0.50-Co_0.50-O催化剂活性最高,反应2h后5-HMF转化率为42.6%,DFF选择性高达98.0%。结果表明,Mn_0.50-Co_0.50-O复合氧化物中钴氧化物的引入可形成CoM_nO_3相态,使催化剂表面Mn~(4+)/Mn~(3+)比例和暴露的晶格氧浓度显著提高,具有更高的表面氧移动性,从而提高催化活性。另外,Mn_0.50-Co_0.50-O复合氧化物可以循环再生5次而催化活性无明显降低,表明其具有优异的稳定性。为提高M_nO_x基催化剂活性组分的利用效率,通过煅烧对载体二氧化钛(P25)进行表面改性,然后采用等体积浸渍法制备得到一系列M_nO_x/P25-a-b催化剂(a,b分别为煅烧处理的温度和时间)。当P25在600℃下煅烧5 h后所得到的M_nO_x/P25-600-5h催化剂表现出最高的活性,2 h内获得33.2%的5-HMF转化率及97.0%的DFF选择性,该活性约为M_nO_x/P25的2倍。实验结果表明,600℃煅烧处理P25后可使其表面可获得最优的锐钛矿/金红石相态比例,有助于提高催化剂的氧移动性,进而获得高催化活性;同时qF烧处理后表面酸性位数目会明显降低,减少反应过程中副反应的发生,从而提高DFF的选择性。
[Abstract]:Biomass, as a clean renewable resource and a substitute for fossil energy, is an important component of sustainable energy systems in the future. A series of platform compounds were obtained by chemical conversion, such as 5-hydroxymethylfurfural succinic acid, 5-HMFs, and so on. Then various kinds of high added value chemicals and fuels were synthesized by catalytic conversion. The products of oxidation reaction of 5-HMF, 2HMF, FDCA and DFF, have important industrial application value. In recent years, extensive attention has been paid to the problems of introducing strong alkali, high cost of noble metal catalysts and low utilization of active components of non-noble metal catalysts in the study of 5-HMF selective oxidation reaction. The Au-Pd alloy catalysts supported on basic zinc carbonate (ZOC) and MnOx / MnOx catalysts supported on Au-PD / ZOC / Mn-Co-O oxides and modified titania P25) were synthesized respectively. The activity of the corresponding catalysts in the selective oxidation reaction of 5-HMF was investigated, and the phase composition of the catalysts was also investigated. The main contents of this paper are as follows: in order to avoid the use of strong alkaline reaction medium, ZOC support was synthesized by hydrothermal method. Then the Au-Pd/ZOC alloy catalyst was prepared by deposit-precipitation method. The FDCA yield of 99% can be obtained by catalytic selective oxidation of 5-HMF under weak alkalinity. The characterization results show that the synergistic effect between au and PD formed by the homogeneous dispersion of au and PD on the ZOC supports is helpful to improve the catalytic effect. At the same time, it was found that the order of activity of the catalyst was consistent with the pH value of aqueous solution of the corresponding carrier. The results show that the surface acid-base property of the support has an important effect on the catalytic activity. In addition, the weak base environment is beneficial to stabilize the ZOC support, improve the stability of the Au-Pd/ZOC, and reduce the activity of the Au-Pd/ZOC for 7 times. In view of the high cost of the noble metal catalyst, Mn-Co-O composite oxide catalysts were synthesized by liquid-phase mixed solid phase calcination method, and their activity was much higher than that of single M _ S _ O _ s _ 2 and Cos _ 3O _ 4 prepared by the same method. When the molar ratio of Mn/Co was 1 and the calcination temperature was 400 鈩，

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