【作者】 冯博；

【导师】 侯震山；

【作者基本信息】 华东理工大学 ， 工业催化， 2011， 博士

【摘要】 本文首先合成出双齿氮配体功能化的聚乙二醇作为Pd纳米粒子的稳定剂,采用不同的还原方法制备出一系列Pd纳米粒子,在绿色溶剂(聚乙二醇、水相)中进行醇类的需氧氧化反应,通过一系列表征手段如UV-Vis, XRD, TEM, XPS等和催化活性的测试,探索Pd纳米粒子的性质与其催化活性之间的关系；同时,将功能化的聚乙二醇与醋酸钯形成络合物催化剂用于端烯烃的氧化反应中,调控其氧化产物的选择性,详细考查其反应动力学,并对反应机理进行探索；然后,以PVP为稳定剂制备出水溶性的Ru纳米粒子,以碱性离子液体为添加剂,在水相中实现醇类的脱氢反应。通过研究主要得出以下结论：(1)双齿氮配体功能化的聚乙二醇对稳定Pd活性物种(Pd(0)纳米粒子和Pd(II))起着至关重要的作用。用其作为保护剂稳定的Pd纳米粒子在PEG和水相中醇类的氧化反应中,至少可以循环四次,并未发现Pd纳米粒子的聚集和流失；其与Pd(II)形成的络合物在烯烃的氧化反应中也表现出很好的稳定性,可循环使用十二次,仍能保持其络合物的结构。通过UV-Vis光谱和XPS分析发现,PEG负载的双齿氮配体与Pd物种之间存在比较强的电子相互作用,从而导致了Pd催化剂的高稳定性。(2)Pd纳米粒子的性质(颗粒大小和表面性质)可以通过改变配体保护剂的用量和还原剂的种类来控制,并且其性质对催化活性有很大的影响。以功能化的聚乙二醇为稳定剂,通过改变还原条件(还原剂的种类、稳定剂的量)制备出一系列的Pd纳米粒子。TEM、XPS分析发现,还原剂的种类对Pd纳米粒子的表面氧化态有很大的影响,采用强还原剂如H2和NaBH4时,Pd纳米粒子的表面主要呈现出还原态的Pd(0),而采用乙醇和苯甲醇作为还原剂时,Pd纳米粒子的表面有很大部分未还原的Pd(II)。通过改变稳定剂的量可以控制Pd纳米粒子的大小,随着稳定剂的增加,Pd纳米粒子的尺寸逐渐减小。通过将Pd纳米粒子的性质与其催化氧化醇类的活性相关联,发现在目前的体系中,Pd(0)是催化活性物种；Pd纳米粒子的催化活性是其颗粒大小、表面氧化态和稳定剂的量共同作用的结果。(3)实现了无氯无碱中性条件下水相中催化氧化苯乙烯及其衍生物生成相应的醛的反应。双齿氮配体功能化的聚乙二醇与Pd(OAc)2形成的络合物催化氧化苯乙烯生成苯甲醛,转化率可达98.0%,选择性为82.0%。通过对反应动力学、氧气压力对反应的影响以及氧气消耗量与底物转化量之间的关系的详细考察,发现Pd(11)是催化活性物种,同时推测出不同于传统Wacker氧化的反应机理,生成醛类的主要原因是形成的环状中间物种的不同的降解路径导致。(4)首次实现了水相中醇类的脱氢反应。以PVP稳定的Ru纳米粒子作为催化剂,碱性离子液体作为添加剂,水相作为反应介质,在N2气氛下,回流条件下,对芳香醇类和烯丙基醇类都有比较高的催化活性,但对于脂肪醇类活性比较低；催化剂循环使用六次,活性并未降低,仍然能够保持比较好的稳定性。(5)本论文涉及的几个催化体系均为环境友好的绿色催化体系,从催化剂的设计、溶剂的选择、反应的原子经济性以及产物的分离和催化剂的循环使用角度都符合绿色化学发展的要求,为绿色反应体系的设计提供了一定的理论基础。更多还原

【Abstract】 This work included the design, characterization and catalytic application of the soluble metal salt/nanoparticles coordinated/stabilized by the functionalized-poly(ethylene glycol) molecules. Firstly, the palladium nanoparticles catalysts were demonstrated for aerobic oxidation of alcohols in poly(ethylene glycol) and aqueous phase; the relationship between the catalytic performance of Pd nanoparticles and its properties was investigated in detailed. Second, an environmentally benign water-soluble Pd(II) complex was developed as a catalyst for the selective aerobic oxidation of styrene to benzaldehyde in high selectivity without any additives in the aqueous phase. Finally, PVP-stabilized ruthenium nanoparticles with [BMMIM]OAc as an additive were utilized as an efficient and reusable catalyst for the oxidant-free dehydrogenation of alcohols in water.(1) The bidentate nitrogen ligand-functionalized-PEG played an important role in stabilizing and immobilizing catalytically active palladium(0) and Pd(Ⅱ) species. Pd species stabilized by the functionalized PEG showed superior stability, and could be reused several times in the oxidation of alcohols or olefins without losing catalytic activities. The excellent stability attributed to the strong electronic interaction between the bidentate nitrogen ligand and Pd species.(2) The particle size and surface properties of the generated palladium nanoparticles can be controlled by varying the amount of protective ligand and the kinds of reducing agents and its properties played very important roles in affecting catalytic performance. The particle size decreased with increasing the amount of the functionalized PEG. The surface composition of the nanoparticles can also be tuned by adopting appropriate reducing agents in the preparation of nanoparticles. By relating catalytic activity to the properties of Pd nanoparticles, we found that the metallic palladium was the active species for benzyl alcohol oxidation in the present system, moreover, the catalytic performance depended strongly on the properties (size and oxidation state) of Pd nanoparticles.(3) Selective oxidation of styrene to benzaldehyde was carried out in aqueous phase by using a green and water-soluble palladium(Ⅱ) complex as a catalyst under neutral, chloride and base-free conditions. The water-soluble Pd(Ⅱ) complex was proved to be stable and highly catalytically active under the present conditions. In particular, the catalyst was easily recovered and could be reused at least twelve times without significant decrease in catalytic performance. UV-Vis spectra indicated that Pd(Ⅱ) complex might serve as the true catalytically active species in the present system and the reaction mechanism different from Wacker Oxidation was proposed.(4) The oxidant-free dehydrogenation of alcohols was developed in water for the first time. The Ru nanoparticles were active for the reaction under N2 atmosphere at reflux conditions for 24 h, giving benzaldehyde in 99% yield together with the generation of H2, where RuCl3 exhibited lower catalytic activity for benzyl alcohol dehydrogenation under the same reaction conditions. The base additive played an important role in effecting catalytic activies. The catalyst could be reused six times without losing catalytic activities, but showed poor activities in the dehydrogenation of aliphatic alcohols.(5) The several catalytic system designed were green, and these results will also contribute to the development of efficient and environmentally friendly catalysts for various organic reactions.更多还原