纳米二氧化铈的制备、表征及其催化串联反应研究

发布时间：2018-03-07 11:46

本文选题：二氧化铈　切入点：氧空位　出处：《大连理工大学》2016年博士论文　论文类型：学位论文

【摘要】：二氧化铈作为催化剂和催化剂载体,广泛应用于可再生能源生产、环境污染治理以及精细化学品合成等领域。二氧化铈优异的催化性能归因于其独特的氧化还原性和适宜的酸碱性,而这些性质通常与其结构中氧空位的性质密切相关。本论文通过形貌选择合成、控制还原和金属离子掺杂等方法实现了二氧化铈中氧空位性质的调变,并探索了缺陷二氧化铈作为一种多功能催化剂在氧化缩合反应以及Prins缩合-水解等串联反应中的应用,系统地研究了氧空位浓度变化对催化剂氧化还原性以及酸碱性的影响,建立了氧空位浓度变化与催化性能之间的关系。主要研究结果如下:通过形貌控制,制备出了棒状、立方体和八面体三种不同形貌的CeO_2催化剂。Raman光谱显示,这三种形貌的CeO_2上的氧空位浓度不同,其中棒状CeO_2催化剂上氧空位浓度最高。制备出的二氧化铈能催化串联反应苯甲醇与苯胺串联氧化缩合制备亚胺类化合物(N-苯亚甲基苯胺)。该反应首先需要将苯甲醇氧化为苯甲醛,继而与苯胺发生缩合生成产物。反应过程中,催化剂的氧空位浓度和氧化还原性至关重要。二氧化铈作为一种氧化-碱催化双功能催化剂,能有效催化苯甲醇与苯乙酮氧化-Aldol缩合制备α,β-不饱和酮(查尔酮)。通过原位屏蔽和动力学实验,确证该串联反应中苯甲醇的氧化发生在CeO_2的氧化还原位点上,而苯甲醛与苯乙酮之间的Aldol缩合反应发生在CeO_2的碱位点上,其中碱位点上发生的Aldol缩合是反应的决速步。通过Raman光谱和CO_2-TPD表征发现,棒状CeO_2催化剂上氧空位浓度和碱位点浓度最高,在苯甲醇与苯乙酮的氧化-Aldol缩合反应中表现出最佳的催化活性。二氧化铈还可作为一种氧空位诱导的耐水Lewis酸催化剂,催化异丁烯与HCHO水溶液间的Prins缩合-水解反应。通过形貌选择合成和控制还原温度,对二氧化铈氧空位浓度进行调变。通过Raman光谱、NH3-TPD、31P-NMR和吡啶红外等表征对催化剂氧空位浓度和酸性质进行表征,发现二氧化铈氧空位诱导的酸位点主要为弱的Lewis酸,且二氧化铈中氧空位浓度越高,催化剂的Lewis酸位点浓度越高,Prins缩合-水解反应活性越高。通过Al、Zr、Eu、Pr和La等金属离子的掺杂,实现了对CeO_2氧空位浓度的调变。HAADF-TEM、吡啶吸附红外、Raman光谱表征表明,Pr的掺杂产生了更多的氧空位,使得催化剂Lewis酸浓度增加。Pr高度分散的掺杂CeO_2能高效催化异丁烯与HCHO水溶液之间的Prins缩合-水解反应。应用DFT对Prins缩合-水解反应过程中两种底物分子的吸附进行计算,确证HCHO的吸附活化是该反应的关键步骤,Pr的掺杂增强了 HCHO在催化剂表面Ce-O位上的吸附活化。
[Abstract]:As catalyst and catalyst carrier, cerium oxide is widely used in renewable energy production. The excellent catalytic performance of cerium oxide is attributed to its unique redox and suitable acidity and alkalinity. These properties are usually closely related to the properties of oxygen vacancies in the structure. In this paper, the properties of oxygen vacancies in cerium oxide have been adjusted by means of morphology selective synthesis, controlled reduction and doping of metal ions. The applications of defective cerium oxide as a multifunctional catalyst in the oxidative condensation reaction and the series reaction such as Prins condensation and hydrolysis were investigated. The effects of the oxygen vacancy concentration on the redox and acidity and alkalinity of the catalyst were systematically studied. The relationship between oxygen vacancy concentration and catalytic performance was established. The main results are as follows: by controlling the morphology, three kinds of CeO_2 catalysts with different morphologies, such as rod, cube and octahedron, were prepared. The oxygen vacancy concentrations on the three morphologies of CeO_2 are different, The prepared cerium oxide catalyst can catalyze the series reaction of benzyl alcohol and aniline in series to produce imines, N-phenylene methylaniline. Alcohol is oxidized to benzaldehyde, In the process of reaction, the oxygen vacancy concentration and redox activity of the catalyst are very important. Cerium oxide is a bifunctional oxidation-alkali catalyst. 伪, 尾 -unsaturated ketone was prepared by condensation of benzyl alcohol with acetophenone. The in situ shielding and kinetic experiments confirmed that the oxidation of benzyl alcohol occurred at the redox site of CeO_2. The Aldol condensation reaction between benzaldehyde and acetophenone occurs on the base site of CeO_2, in which the Aldol condensation at the base site is the fast step of the reaction. The oxygen vacancy concentration and base site concentration on the rod-like CeO_2 catalyst are the highest, showing the best catalytic activity in the oxide-Aldol condensation reaction of benzyl alcohol with acetophenone. Cerium oxide can also be used as a water-tolerant Lewis acid catalyst induced by oxygen vacancy. Catalytic Prins condensation and hydrolysis between isobutene and HCHO aqueous solution. The oxygen vacancy concentration and acid properties of the catalyst were characterized by Raman spectra, NH _ 3-TPDN _ 3P-NMR and pyridine infrared spectra. It was found that the acid sites induced by cerium oxide oxygen vacancies were mainly weak Lewis acids. The higher the concentration of oxygen vacancy in cerium oxide is, the higher the concentration of Lewis acid sites in the catalyst is. The modulation of oxygen vacancy concentration of CeO_2. HAADF-TEM has been realized. The IR spectra of pyridine adsorption show that more oxygen vacancies are produced by the doping of pr. Doping CeO_2, which makes the concentration of catalyst Lewis acid increase. Pr highly dispersed, can efficiently catalyze the Prins condensation hydrolysis reaction between isobutene and HCHO aqueous solution. The adsorption of two kinds of substrate molecules in the process of Prins condensation and hydrolysis is calculated by DFT. It is confirmed that the adsorption and activation of HCHO is a key step of the reaction. The doping of pr enhances the adsorption and activation of HCHO on the surface of Ce-O on the catalyst surface.
【学位授予单位】：大连理工大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O643.36;TQ133.3

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