【作者】 王菲菲；

【导师】 杨林；

【作者基本信息】 河南师范大学 ， 物理化学， 2014， 博士

【摘要】 醇的催化氧化是有机合成化学中研究较多的一种官能团转变过程，也是精细化学合成相应羰基化合物的主要过程。目前这些化合物每年在世界范围内以百万吨的产量进行生产，范围包括从大宗化学品到医药等，其中芳香醇的氧化也是精细化学合成的一个重要组成部分，但如何通过一些简单、易行的方法将醇快速、有效的选择氧化为醛或酮一直是研究的热点之一。在对芳香醇等醇类的选择性氧化中，氧化剂的来源也是一个需要着重考虑的问题。随着绿色化学的大力发展和全球环保意识的增强，传统的氧化方法已不能满足工业生产的需求。因此一些价格低廉、环境友好的“绿色氧化剂”——空气、氧气或过氧化氢便成为了氧化反应最理想的氧源。同时，负载型贵金属催化剂以其优异的催化活性和耐高温、抗氧化、耐腐蚀等优良特性，成为了醇选择氧化反应最重要的催化剂材料，其中贵金属Pd由于具有资源丰富、价格低廉、稳定性好等优点，应用也越来越广泛。因此如何设计一种适用醇的催化氧化反应的新的或改进的负载型贵金属催化剂是目前该方面的国际研究前沿。基于负载型贵金属催化剂的研究现状，负载型贵金属催化剂的研究趋势大致可以从三个方面来设计和考虑改进：（1）贵金属的可控合成。大量研究表明，纳米粒子的催化活性和选择性在很大程度上与纳米粒子的尺寸、形貌等性质相关，随着金属粒子相关理化性质的变化，催化性质也会随之变化。因此可以通过对制备方法的改进直接对贵金属的尺寸、形貌和晶面结构等进行可控合成，制备出粒径小、分散度好、低负载量、高活性、高稳定性的负载型贵金属催化剂；（2）选择合适的载体。载体不仅是负载型贵金属催化剂中活性组分的承载者，研究证明合适的载体还可以提高贵金属在载体上的分散度。同时载体也有一定的活性，可以与活性组分发生强强相互作用。在有些体系中，载体与活性组分能形成化合物。所有这些对催化剂的吸附性能以及催化性能将产生影响；（3）添加有效的助催化剂。助剂的加入能够影响催化剂中活性组分的离子价态及分布、晶体与表面结构、酸碱性等，从而影响催化剂的活性、选择性以及寿命等。基于上述研究背景，本论文主要内容有以下几方面：一、具有高能量晶面的Pd基催化剂的合成及对芳香醇氧化性能的影响。已知合成的常见Pd纳米颗粒的晶面主要是{111}晶面，在本章中我们利用层层自组装机理制备的花状羟基磷灰石（F-HAP）做载体，合成了鲜见报道的{110}晶面占主导的Pd纳米催化剂，同时研究了不同形貌HAP载体和不同合成方法对Pd基纳米催化剂的合成和DL-sec-苯乙醇无溶剂催化氧化性能的影响。研究表明用花状羟基磷灰石（F-HAP）做载体，采用简单的一步溶剂热法制备的具有高能量晶面的Pd{110}纳米催化剂（Pd/F-HAP）具有良好的催化活性和稳定性，在403K，反应1.5h后，对DL-sec-苯乙醇无溶剂氧化反应的转换频率值(TOF)可达12753h-1。接着进一步研究了Pd/F-HAP催化剂的催化机理，通过中间体的监测，提出了与文献报道的Pd{111}晶面不同的催化机理，即氧活化机理。理论计算结果支持了这一机理，计算结果表明O2在Pd{110}晶面上更易解离，而且Pd作为活性中心，其高能量晶面的存在更有利于醇的选择性氧化。二、不同形貌CeO2载体对Pd基催化剂的合成及芳香醇氧化性能的影响。以己二酸为结构导向剂，用简单的一步溶剂热法合成了具有分级结构的介孔CeO2中空球，其平均粒径约为135nm，并由平均尺寸为3nm的小颗粒组成，孔隙大小为3.3-4.2nm，壁厚约为25nm，并推测其形成机理为自组装和奥斯特瓦尔德熟化相结合机理。在此实验的基础上，我们选用了三种不同形貌的CeO2做载体，分别为：介孔中空球，介孔球和块状材料，合成了相应的三种Pd/CeO2催化剂，分别为Pd/CeO2-5h，Pd/CeO2-1h，Pd/CeO2-商品。性能测试结果表明Pd/CeO2-5h在403K下反应2.5h后，对DL-sec-苯乙醇的转化率即可达到92%以上。结果表明高比表面积的介孔CeO2中空球能够为反应物提供更多的活性位来发生吸附和活化反应，且有助于金属分散，并有效地提高催化剂和反应物之间的接触，从而提高其催化活性。三、不同形貌碳载体对Pd基催化剂的可控合成及芳香醇氧化性能的影响。一方面，我们比较了不同制备方法对Pd/XC-72催化剂催化性质的影响。结果显示，与传统的浸渍法和甲醛还原法相比，用以乙二醇为溶剂、谷氨酸为连接剂的溶剂热法可以有效地控制Pd的反应速率和Pd纳米颗粒的晶体生长速率，进而制备出Pd粒径较小，颗粒分散较均匀的Pd/XC-72催化剂；另一方面，我们以Vulcan XC-72、CNT和石墨（graphite）三种碳材料为载体，采用简单的一步溶剂热法制备了不同碳载体负载的Pd基催化剂，从中考察了载体不同对苯甲醇无溶剂液相氧化制苯甲醛催化性能的影响。研究表明制备的Pd/XC-72/Glu催化剂在无溶剂条件下，403K反应5h后，苯甲醇的转化率为85.5%。远远高于Pd/CNT/Glu（60.2%）和Pd/graphite/Glu（13.9%）催化剂对苯甲醇的转化率。四、非贵金属助剂对Pd基催化剂的合成及芳香醇氧化性能的影响。在本章中，我们以DL-sec-苯乙醇氧化制苯乙酮做为目标反应，根据d带空穴数的多少，选用非贵金属Cr、Mn、Hg做为Pd/XC-72催化体系的助催化剂，对比了PdCr/XC-72/Glu、PdMn/XC-72/Glu和PdHg3.5/XC-72/Glu这三种催化剂在氧气气氛下对DL-sec-苯乙醇的无溶剂催化氧化反应；实验结果表明PdCr/XC-72/Glu催化剂在无溶剂条件下，403K反应3h后，DL-sec-苯乙醇的转化率为91%，远远高于PdMn/XC-72/Glu（53%）和PdHg3.5/XC-72/Glu（32%）催化剂对DL-sec-苯乙醇的转化率。进一步从能带理论和密度泛函理论解释了PdCr/XC-72催化剂催化活性较好的原因：即d带空穴数较多的Cr的引入提高了活性金属d空态密度和费米能级处的态密度，增加了整个合金纳米颗粒在XC-72载体表面的分散度，从而提高了PdCr/XC-72/Glu催化剂的催化活性。更多还原

【Abstract】 The oxidation of alcohols to their corresponding aldehydes and ketones is one of the most importantfunctional group transformation processes in organic synthetic chemistry. It is of significant importance inorganic chemistry, both for fundamental research and industrial manufacturing. The world-wide annualproduction of carbonyl compounds is over107tonnes and many of these compounds are produced from theoxidation of alcohols，especialy aromatic alcohols. But how to find some simple and feasible methods foroxidation of alcohols to aldehydes or ketones quickly and effectively has been one of research hotspots.Usually, the oxidation of alcohols is traditionally carried out with stoichiometric amounts of oxidants.These methods often require one or more equivalents of these relatively expensive oxidizing agents. Someof these processes also generate equal amounts of metal waste. Therefore, using air or pure dioxygen (O2)that is cheaper and amity to the environment as oxidants, is of paramount importance for both economicand environmental reasons. Besides, the supported noble metal catalysts become the most importantcatalyst for the selective oxidation of alcohols because of its excellent catalytic activity, high temperatureresistance, oxidation resistance, corrosion resistance and other excellent features, especialy the supportedPd-based catalyst is becoming more and more widely applied due to its advantages of rich resources,relative low cost and good stability.So how to design new and improved supported noble metal catalysts which are suitable for specificreactions is one of the hot research topics that a lot of scientific research workers are looking for.Considering the composition of supported noble metal catalysts, it can be designed and improved fromthree aspects:(ⅰ) controllable synthesis of noble metal nanoparticles. A lot of research shows the catalyticactivity and selectivity of the NPs largely depend on the size, shapes and other properties of the particles.With the change in related physical and chemical properties, the catalytic property also changes. So directlyby improving the preparation method, you can get supported noble metal catalysts with small particle size,good dispersion, low load and high stability;(ⅱ) choose appropriate supports. It has been proved that theappropriate suport can improve the dispersion of noble metals on it. Support also has a certain activitywhich can make strong interaction with noble metals. In some systems, support and active component can form compounds. All these will have an impact on the adsorption performance and catalytic properties ofthe catalysts;(ⅲ) add promoters. After adding certain promoters, supported noble metal catalysts arelikely to change on the chemical composition, ion valence, acid-base property, crystal structure, surfacestructure, pore structure, decentralized state, the mechanical strength and so on, thus affecting the catalyst’sactivity, selectivity and lifetime.Based on the above reasons and the main research of this paper, this paper mainly discuss from thefollowing points:Firstly, synthesis of Pd catalysts with high energy facets and its effect on the properties of alcoholoxidation. Pd nanoparticles enclosed by low energy facets {111} are commonly prepared. In this chapter,Pd with high energy facets {110} supported on F-HAP was successfully prepared by a facile solvothermalmethod. The catalytic results for the solvent-free oxidation of DL-sec-phenethylalcohol by O2indicatedthat the nanocatalysts with high energy facets were powerful tools for enhancing their catalytic activity andstability. Its TOF was12753h-1at403K,1.5h. Then the Pd/F-HAP catalytic mechanism was further studied.Through monitoring the intermediate, we put forward the oxygen activation mechanism which wasdifferent from the literatures’. It was also consistent with the theoretical calculation result. The calculationresults showed that O2on the Pd {110} faces were more likely to disintegrate, and the high energy facets ofPd were more advantageous to the existence of selective oxidation of alcohols. Meanwhile, the choice ofF-HAP as a catalyst support was beneficial to the improvement of the catalytic activity and repeatability ofPd nanoparticles.Secondly, effect of the morphology of CeO2support on the activity of Pd/CeO2catalysts for alcoholoxidation. Herein, porous CeO2hollow nanospheres composed of small nanoparticles was controllablyprepared through a simple one-step solvothermal reaction with adipic acid. It was characterized that theporous CeO2hollow nanospheres composed of small nanoparticles with an average diameter of3nm havea uniform size of135nm and a wall thickness of25nm, and a self-assembly process coupled with anOstwald ripening mechanism for the hollow structures formation was proposed based on a series oftime-dependent HRTEM observations. Based on this experiment, We chosed porous CeO2hollownanospheres, porous CeO2nanospheres and bulk CeO2as supports to prepare Pd/CeO2-5h, Pd/CeO2-1h andPd/CeO2-goods respectively. The catalytic performance of these catalysts showed that the Pd/CeO2-5h catalyst had the highest conversion of DL-sec-phenethylalcohol (up to92%) at403K,2.5h. The resultsshowed that the special structure of the porous CeO2hollow nanospheres and its high specific surface areacould provide more active sites for the reactants to adsorb and activate. Moreover, it was helpful to themetal dispersion, and effectively improved the contact between catalyst and reactant, thus improved itscatalytic activity.Thirdly, effect of the morphology of carbon support on the activity of Pd/C catalysts for alcoholoxidation. On the one hand, we compared the different preparation methods on the influence of thePd/XC-72catalyst properties. Compared with traditional impregnation method and formaldehyde reductionmethod, the simple one-step solvothermal method in which ethylene glycol was used as a reductant andglutamate was employed as an additive could effectively control the reaction rate and the crystal growthrate of Pd nanoparticles, and then the Pd/XC-72catalyst with small and uniformly dispersed Pd particlewere prepared. On the other hand, Pd/XC-72/Glu, Pd/CNT/Glu and Pd/graphite/Glu catalysts with differentsupports were prepared by simple one-step solvothermal method in which ethylene glycol was used as areductant and glutamate was employed as an additive．The catalytic results of these catalysts forsolvent-free oxidation of benzyl alcohol with molecular oxygen showed that the catalytic activities of Pdwere influenced by the different supports, and The Pd/XC-72/Glu catalyst showed the highest conversionof benzyl alcohol (up to85.5%) at403K,5h, which was much higher than that of Pd/CNT/Glu (60.2%) andPd/graphite/Glu (13.9%).Fourthly, effect of non-noble metal promoters on the synthesis and catalytic performance of supportedPd-based catalysts. In this chapter, the solvent-free oxidation of DL-sec-phenethylalcohol was selected as atarget reaction, and Cr, Mn, Hg were chosen to be non-noble metal promoters. It was indicated that thecatalytic performance of Pd/XC-72/Glu catalyst was improved significantly by the addition of a secondmetal promoter. The test results of solvent-free oxidation of DL-sec-phenethylalcohol overPdCr/XC-72/Glu catalyst showed that its alcohol conversion is91%at403K,3h, which is much higherthan that of PdMn/XC-72/Glu (53%) and PdHg3.5/XC-72/Glu (32%). Based on the band theory, the statedensity and d belt hole of PdCr, PdMn and PdHg were calculated by the first principles calculation basedon density functional theory. The calculation results indicated the electronic state of Pd atom was optimizedin the presence of Cr. Thus, the activity and selectivity of PdCr/XC-72/Glu catalyst were improved.更多还原