二氧化钛可见光光催化醇的选择氧化及其机理研究

发布时间：2018-08-11 14:49

【摘要】：以分子氧为氧化剂,在非常温和条件下实现将醇选择氧化为醛或酮是一个非常具有挑战的课题。利用二氧化钛紫外光光催化可以在室温的条件下实现分子氧的活化进而进行醇的选择氧化,因此受到科学研究者的广泛关注,目前已有许多成果。但是利用可见光光催化实现醇的选择氧化仍然是一个难题。在论文中我们以分子氧或空气中的分子氧为氧化剂,采用染料敏化二氧化钛的策略在可见光照射下成功实现了醇选择氧化为相应的醛或酮的过程,取得了如下所示的两方面的进展:(1)利用曙红染料敏化锐钛矿二氧化钛可以吸收可见光,通过2,2,6,6-四甲基哌啶-1-氧自由基(TEMPO)氧化还原中介引发相应的醇的选择氧化反应。在绿光LED照射下,染料敏化二氧化钛的可见光光催化过程可以与TEMPO的催化氧化循环进行协同作用。TEMPO是一种实现醇类选择氧化的有效催化剂,这可以进一步以分子氧为氧化剂实现醇的选择氧化。动力学和同位素效应(KIE)的结果表明醇的Ca-H的活化是反应的决速步。这表明可见光光催化与TEMPO催化的协同作用在氧化转化过程中具有很大的潜力。(2)实现了以空气中的分子氧为氧化剂,茜素红染料为敏化剂在二氧化钛表面有效地收集可见光以诱导直接的光催化醇的选择氧化反应。二氧化钛为茜素红的光催化反应提供了平台,在电子转移和氧活化中起着氧化还原活性的作用。在这个可见光光催化体系中,活性醇如苯甲醇及其衍生物可以转化为相应的醛,具有良好的转化率和优异的选择性。其它代表性的醇如烯丙基醇,仲醇和伯醇也有不错的转化率和选择性。结果表明选择合适的染料分子与二氧化钛结合可以直接用来实现挑战性的有氧氧化反应。总之,我们利用染料敏化二氧化钛的可见光光催化体系,在室温下以纯氧或空气为氧化剂,实现了多相可见光催化选择性氧化醇类为醛或酮的体系,只有水作为副产品形成,实现了高效和高选择性的产物的形成,是到目前为止最为有效的多相光催化的有机转化体系。
[Abstract]:The selective oxidation of alcohols to aldehydes or ketones under very mild conditions with molecular oxygen as oxidant is a challenging subject. Ultraviolet photocatalysis of titanium dioxide can activate molecular oxygen at room temperature and then selective oxidation of alcohols, so it has been widely paid attention to by scientific researchers and many achievements have been made. However, the selective oxidation of alcohols by visible light catalysis is still a difficult problem. In this paper, the selective oxidation of alcohols to corresponding aldehydes or ketones was successfully realized by using the strategy of dye sensitized titanium dioxide under visible light, using molecular oxygen or oxygen in air as oxidant. Two advances have been made as follows: (1) the selective oxidation of alcohols can be initiated by using the eosin dye sensitized anatase titania to absorb visible light and to initiate the selective oxidation of alcohols through the redox intermediation of (TEMPO). Under green LED irradiation, the visible photocatalytic process of dyestuff sensitized titanium dioxide can be synergized with the catalytic oxidation cycle of TEMPO. Tempo is an effective catalyst for selective oxidation of alcohols. The selective oxidation of alcohols can be realized by using molecular oxygen as oxidant. The kinetic and isotopic effects of (KIE) indicate that the activation of Ca-H of alcohols is a critical step in the reaction. This indicates that the synergistic effect of visible light catalysis and TEMPO catalysis has great potential in the process of oxidation and conversion. (2) the molecular oxygen in air is used as oxidant. Alizarin red dyes were used as sensitizers to effectively collect visible light on the surface of titanium dioxide to induce direct photocatalytic selective oxidation of alcohols. Titanium dioxide provides a platform for the photocatalytic reaction of alizarin red and plays an active role in electron transfer and oxygen activation. In this visible light catalytic system, active alcohols such as benzyl alcohol and its derivatives can be converted to corresponding aldehydes with good conversion and excellent selectivity. Other typical alcohols such as allyl alcohols, secondary alcohols and primary alcohols also have good conversion and selectivity. The results show that the suitable dye molecules can be directly combined with titanium dioxide to realize the challenging aerobic oxidation reaction. In a word, we have realized the selective oxidation of alcohols to aldehydes or ketones under room temperature with pure oxygen or air as oxidant, using dye sensitized TIO _ 2 as visible light catalysis system. Only water is formed as by-product. The formation of highly efficient and highly selective products is the most effective organic conversion system of multiphase photocatalysis up to now.
【学位授予单位】：华中师范大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O621.251

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