羧基化碳材料在酸催化反应中的应用

发布时间：2018-03-18 02:13

本文选题：羧基化碳催化剂　切入点：釜式蒸汽处理　出处：《中国科学技术大学》2017年博士论文　论文类型：学位论文

【摘要】：探索并应用非金属催化剂,作为对传统金属基工业催化剂的补充和替代选择,具有广阔的研究空间和市场前景,近年来已经逐渐成为了学术界和工业界的共同热点。在非金属催化剂中,碳基固体酸催化剂具有酸性位种类多样、骨架具有丰富的被修饰可能性、可以调节表面亲疏水性调控对底物分子的吸附、生物相容性好并且更容易绿色地回收与降解的独特优势。碳材料表面的酸性位对负载金属活性位也起到了非常关键的作用,对酸性位的研究也会对负载金属催化剂的制备及研究金属与载体间的相互作用提供指导。本论文以碳材料上的羧基基团为目标活性位,以酸催化反应为核心应用目标,分别从尝试优化引入羧基的合成方法,探索羧基化学环境对活性位构效关系的影响,表征碳碎片化学结构以推测碳材料表面化学性质这三个角度,对羧基化碳材料(主要是碳纳米管)在酸催化反应中的应用进行了研究。得到的主要结论如下:(一)发明了一种以釜式硝酸蒸汽氧化装置为核心的气相氧化方法,不受沸点限制。通过提升氧化温度,可以在更短的时间内达到更强的氧化效果,并大幅降低了硝酸的用量。因为氧化刻蚀产生的碳碎片在气相中相对不容易脱离,能够在一定程度上抑制持续刻蚀。当氧化程度增加时,单个羧基的平均催化活性也会随之上升。羧基之间以及硝酸氧化过程中引入的硝基基团可能通过吸电子诱导效应,增强了羧基的酸强度。(二)建立了一套完整的液相反应动力学分析程序,以氧化苯乙烯的酸催化开环反应为探针,通过动力学研究测定了归一化的初始反应速率、反应表观活化能Ea、指前因子A、反应级数等动力学参数。利用指前因子A作为有效酸性位数量的替代描述因子,拟合出求取pKa值的工作曲线,首次得到了碳材料上的羧基的平均拟合pKa值,实现了对不同碳材料羧基酸强度的定量比较。推测羧基化碳材料表面可能存在两种硝基与羧基的相互作用,能够不同程度地增强羧基酸强度,导致硝基基团表现出不同的热稳定性。(三)首次非常清晰地确认了碳材料上羧基、硝基、酸酐、内酯的红外特征峰归属,并且在原位加热的条件下观测到上述官能团的热分解,以及羧基向酸酐和内酯的转化。本论文在一定程度上推进了对于碳基催化剂在酸催化反应中应用的理解,较为深入地研究了羧基酸强度与催化活性的构效关系,初步摸索并证实出了一些对于优化活性位化学环境具有指导意义的化学规律。
[Abstract]:To explore and apply non-metallic catalysts as a supplement and alternative to traditional metal-based industrial catalysts has broad research space and market prospects. In recent years, it has gradually become a common focus of academia and industry. Among non-metallic catalysts, carbon-based solid acid catalysts have a variety of acidic sites, and the skeleton has a rich possibility of modification. It can regulate the adsorption of substrate molecules by surface hydrophobicity, and has the unique advantages of good biocompatibility and easier green recovery and degradation. The acidic sites on the surface of carbon materials also play a very important role in loading metal active sites. The study of acidic sites will also provide guidance for the preparation of supported metal catalysts and the study of the interaction between metals and supports. In this thesis, carboxyl groups on carbon materials are regarded as the target active sites and acid catalytic reactions as the core application targets. In this paper, we try to optimize the synthesis method of introducing carboxyl groups, explore the influence of carboxyl chemical environment on the active structure-activity relationship, and characterize the chemical structure of carbon fragments in order to speculate the surface chemical properties of carbon materials. The application of carboxylated carbon materials (mainly carbon nanotubes) in acid catalytic reaction was studied. Not subject to boiling point. By raising the oxidation temperature, you can achieve a stronger oxidation effect in a shorter time, and greatly reduce the amount of nitric acid, because the carbon fragments produced by the oxidation etching are relatively difficult to detach in the gas phase. The average catalytic activity of a single carboxyl group increases with the increase of oxidation degree. Nitro groups introduced between carboxyl groups and during nitric acid oxidation may be induced by electron absorption. The acid strength of carboxyl group was enhanced. (2) A complete program for the kinetic analysis of liquid phase reaction was established. The initial reaction rate of normalized reaction was determined by kinetic study using the acid catalyzed ring-opening reaction of styrene oxide as the probe. The kinetic parameters such as apparent activation energy (EA), preexponential factor A, reaction order and so on. Using preexponential factor A as an alternative description factor of effective acid sites, the working curve of calculating pKa value is fitted. The average fitting pKa value of carboxyl groups on carbon materials is obtained for the first time, and the quantitative comparison of carboxylic acid strength of different carbon materials is realized. It is inferred that there may exist interaction between two nitro groups and carboxyl groups on the surface of carboxyl carbon materials. Can enhance the strength of carboxylic acid to varying degrees, leading to different thermal stability of nitro groups. (3) for the first time, the infrared characteristic peaks of carboxyl, nitro, anhydride and lactone on carbon materials are confirmed very clearly. The thermal decomposition of the above functional groups and the conversion of carboxyl groups to acid anhydride and lactone have been observed under in situ heating. To some extent, the understanding of the application of carbon-based catalysts in acid catalytic reactions has been advanced. The structure-activity relationship between carboxylic acid strength and catalytic activity was studied in depth, and some guiding chemical laws for optimizing the active site chemical environment were preliminarily explored and confirmed.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O643.36

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