【作者】 王静；

【导师】 贾明君； Werner R.Thiel；

【作者基本信息】 吉林大学 ， 物理化学， 2014， 博士

【摘要】 环氧化合物是一类重要的有机合成中间体和化工原料，广泛应用于石油化工、精细化工、高分子材料及电子工业等领域。烯烃催化环氧化反应是合成环氧化合物的主要途径，相关领域的研究一直倍受关注。作为一类重要的烯烃环氧化催化剂体系，多金属氧酸盐（也称多酸或多金属氧簇，简称POMs）包含多个具有高氧化态的配位金属原子，可以作为优良的多电子受体，且具备良好的电子和质子的传输能力，因此对多种类型烯烃（包括空间位阻较大的缺电子烯烃）环氧化表现出非常优异的催化性能。传统的多金属氧酸盐催化剂大多数是均相的，虽然其催化活性好、效率高，但这类催化剂具有回收困难、成本高等缺点，从而成为阻碍其发展和实际应用的主要因素。相比之下，多相催化剂体系在回收、分离等方面具有显著优势，更加环境友好，是目前研究和开发的重点。近年来，科研工作者们已经开展了大量的关于多金属氧酸盐基多相催化剂的研究工作，并且取得了显著进展。主要的研究思路可以概括为以下四个方面：一是将POMs固载到合适的载体上制备出负载型多相催化剂；二是通过溶胶-凝胶技术，将POMs引入到氧化硅/金属氧化物的骨架中；三是将POMs包裹到金属有机骨架（MOF）中；再就是直接利用多酸与合适的有机组分构筑出具有特定空间（孔）结构的超分子组装体。一般来说，高效、稳定的多金属氧酸盐基多相催化剂体系通常具有以下特点：首先是多金属氧酸盐与载体（有机组分）之间存在适当的相互作用（如：共价键、静电力、氢键等）；其次就是载体材料应该具有较高的比表面积，较大的孔容、孔径以及合适的表面性质（极性和酸碱性）。由此可见，载体（有机组分）的选择会极大影响负载型POMs催化剂的催化性能。基于上述情况，本论文主要以不同方法制备的各种咪唑功能化有机-无机杂化材料为载体，通过静电相互作用，将不同种类的磷钼杂多化合物引入到载体的孔道及表面上，构筑出一系列负载型POMs催化剂体系。考察了这些催化剂在烯烃环氧化反应中的催化性能。结合各种表征手段和反应结果，研究了载体的结构、表面性质（酸碱性和极性）、多酸活性组分和载体之间的相互作用以及多酸的种类对催化剂环氧化性能的影响。同时，针对性能优异的多相催化剂体系考察了烯烃种类、氧化剂类型、溶剂等因素对其催化活性和稳定性的影响。此外，还探讨了催化活性中心性质及催化作用机制等问题。主要研究内容及结果概述如下：一．咪唑功能化介孔材料固载磷钼酸催化剂的制备及环氧化性能研究采用离子交换法，将磷钼酸（PMA）锚定到咪唑类离子液体（IL）功能化的介孔材料上，制备了一系列磷钼酸基杂化材料。介孔载体材料包括纯硅分子筛（SBA-15）、介孔磷酸铝材料（AlPxO, x=0.9,1.0,1.1）和介孔炭（NC-2）。所制备的杂化催化剂在以叔丁基过氧化氢（TBHP）为氧源的环辛烯环氧化反应中，均表现出良好的反应活性和对主产物接近100%的选择性。其中，以介孔磷酸铝（AlP1.0O和AlP1.1O）为载体制备出的催化剂PMA@IL/AlP1.0O和PMA@IL/AlP1.1O的催化活性、稳定性明显优于其它催化剂。各种表征结果证实，相较于AlP0.9O，AlP1.0O和AlP1.1O具有相对较高的比表面积、较大的孔径和孔容、表面存在大量的P–OH，这些因素有利于提高多酸活性组分的固载量、稳定性以及在表面的分散度。此外，这类AlPxO载体骨架中存在的P、Al物种，在稳定活性中心以及辅助活化氧化剂方面能够起到积极作用。另外，还考察了这类催化剂在烯醇环氧化反应中的催化性能。结果表明，催化剂PMA@IL/NC-2能够有效地催化以TBHP为氧源、甲醇为溶剂的几种烯醇（3-甲基-2-丁烯-1-醇、反式-2-己烯-1-醇、香叶醇）的环氧化反应。在极性质子溶剂（甲醇）中，炭载体表面丰富存在的含氧基团，有助于烯醇和催化活性中心有效地接触，同时也有利于环氧化产物从催化剂的表面脱附，从而使催化剂表现出较高的催化活性。二．咪唑基介孔有机硅固载磷钼酸催化剂的制备及烯烃环氧化性能以含有不同量咪唑阳离子（10%和15%）的介孔有机硅（PMO-ILs，分别为a和b）为载体，制备了一类固载化磷钼酸（PMA）多相催化材料（PMA@PMO-ILs，2a和2b）。采用一系列表征技术研究了材料的结构及物理化学性质。结果表明，磷钼酸阴离子通过静电作用被成功固载到PMO-ILs载体的表面和孔道中，且在制备过程中磷钼酸及载体的基本结构均未发生变化。这类PMA@PMO-ILs材料在以TBHP为氧化剂的环辛烯环氧化反应中表现出良好的催化活性和很高的选择性。中断实验结果显示，催化剂的主要活性中心在反应过程中未发生明显流失，且催化剂经多次循环使用后活性及选择性基本保持不变。通过与磷钼酸功能化的SBA-15材料（2c）的催化性能进行对比分析，可以认为PMO-ILs载体上大量存在的咪唑阳离子能有效稳定磷钼酸阴离子，使该类催化剂表现出良好的稳定性。另外，进一步对PMO-IL（a）载体的表面进行了后修饰，即先采用后嫁接法使氨丙基硅烷偶联剂与PMO-IL材料中表面存在的硅羟基发生缩合反应，之后再引入磷钼酸物种制备出表面氨功能化的催化剂（2d）。研究结果表明，氨丙基的引入导致载体的比表面、孔径及孔容均有所降低，并且氨丙基柔性链的存在还在一定程度上阻碍了磷钼酸活性组分与载体表面咪唑阳离子的接触，从而导致2d催化剂的活性和稳定性有所降低。这些结果进一步说明活性组分和载体之间存在合适的相互作用以及载体具有适当的结构是影响负载型POMs催化剂性能的重要因素。三．咪唑基介孔有机硅固载第四周期过渡金属取代的磷钼杂多化合物催化剂的制备及烯烃环氧化性能以咪唑基介孔有机硅PMO-IL（a）为载体，通过静电作用力引入几种过渡金属取代的磷钼杂多化合物，制备了PCoMo11@PMO-IL （3a）、PMnMo11@PMO-IL（4a）、PNiMo11@PMO-IL（5a）和PCuMo11@PMO-IL（6a）等负载型催化剂。ICP-AES、N2吸附-脱附、XRD、FT-IR、UV-Vis及XPS等表征结果证实了杂多阴离子被成功固载到PMO-IL载体上，且在制备过程中杂多阴离子及载体的结构均未发生明显变化。通过以分子氧为氧化剂，异丁醛为共还原剂的烯烃环氧化反应，考察了催化剂的催化性能。结果表明，这些固载化催化材料对多种烯烃（环辛烯、1-辛烯、苯乙烯、环己烯）的环氧化都表现出良好的催化活性。其中，催化剂3a表现出最高的反应活性、环氧化合物的选择性以及循环性。此外，针对3a在不同的催化反应条件下，包括不同反应温度和时间、不同的异丁醛和烯烃摩尔比以及不同氧化剂体系（分子氧和叔丁基过氧化氢）中表现出的催化活性及选择性差异，结合相关文献，推测出这类负载型催化剂在分子氧为氧化剂、异丁醛为共还原剂的条件下，催化烯烃环氧化反应的机理。首先，异丁醛在催化剂中过渡金属物种的引发下转化为酰基自由基；然后，酰基自由基与分子氧结合生成酰基过氧自由基，该酰基过氧自由基会按照不同的历程完成烯烃的选择性氧化。由此可见，这类负载型催化剂结构中含有的过渡金属的种类、价态会直接影响自由基的生成，进而影响烯烃的反应速率以及产物分布。3a结构中存在具有相对较高正电性的CoⅡ，应该是该催化剂表现出相对高活性和高环氧化物选择性的主要原因。更多还原

【Abstract】 Epoxide compounds are useful intermediates and chemical raw materials inorganic synthesis, and widely used for petrochemicals, fine chemicals, polymers andelectronic industry. Epoxidation of olefins is the most important reactions toapproach epoxides. Polyoxometalates (POMs) are a class of early‐transition‐metaloxides, which contain a number of coordinated metal atoms at high oxidation state.They could serve as excellent multi-electron acceptors, possess a good transmissioncapacity of electrons and protons, and exhibit excellent oxidation resistance.Therefore, POMs have shown attractive catalytic performance in the selectiveoxidation of olefins. However, almost all sophisticated POMs or POM-basedepoxidation catalysts are homogenous in essence. Much recent effort has beenfocused on achieving the heterogenization of homogeneous POM catalysts in orderto overcome their drawbacks, separation and recycling problems. Differentpreparation strategies have been developed to obtain heterogeneous POM‐basedcatalyst systems. These include immobilizing POMs on porous support surfaces,incorporating POMs in silica or metal oxide matrices via sol‐gel techniques,encapsulating POMs within nanocages of metal‐organic frameworks, andself‐assembling POMs with organic compounds to form supramolecular structures.To obtain highly efficient and stable POM‐based heterogeneous catalysts, anappropriate interaction between POMs and the support (or host) is usually necessary.This may include covalent bonds, electrostatic binding, hydrogen bonds, and/orother interactions. The support should possess a sufficiently high surface area, a large pore size, and a suitable surface polarity, as these parameters influence thedistribution and accessibility of catalytically active species.Based on the above, in this thesis, the supported POM-based catalysts wereachieved by the electrostatic immobilization of different kinds ofphosphomolybdates on the imidazolium functionalized organic-inorganic hybridmaterials. Their catalytic performances were investigated for the liquid-phaseepoxidation of olefins. Combined with different characterizations and experimentalresults, the effect of structures and surface properties of the supports on the catalyticproperties of POM-based catalysts was studied, and the essence of interactionbetween POM units and supports was also discussed for clarifying the nature ofactive sites and understanding the catalytic reaction mechanism. The main resultsand conclusions are as follows:1. Immobilization of phosphomolybdic acid on imidazolium functionalizedmesoporous materials for catalytic epoxidation reactionsA series of phosphomolybdic acid-based hybrid materials were prepared by ionexchange method, which referred to immobilize phosphomolybdic acid (PMA) onthe imidazolium ionic liquid functionalized supports. These supports includedmesoporous silica materials (SBA-15), mesoporous aluminum phosphate (AlPxO, x=0.9,1.0,1.1) and mesoporous carbon (NC-2). All the resulting hybrid materialsexhibited relatively high catalytic activity and nearly100%selectivity to cycloocteneepoxide in the cyclooctene epoxidation with TBHP as the oxidant. Among them,PMA@IL/AlP1.0O and PMA@IL/AlP1.1O were more active and stable than the otherthree kinds of hybrid materials. Combined with different characterizations, therelatively high catalytic performance of these two catalysts should be mainlyattributed to the characteristics of the AlPxO (x=1.0,1.1) supports, such as suitablestructures, compositions and surface properties.In addition, the catalytic activity of these PMA-based catalysts also beeninvestigated in the epoxidation of a wide range of allylic alcohols(3-methyl-2-butene-1-ol, trans-2-butylethylene-1-ol and geraniol). It was found that PMA@IL/NC-2acted as an efficient catalyst under TBHP and methanol system.This could be ascribed to the presence of the oxygen groups on the surface of NC-2support, which have improved the accessibility between allylic alcohols and PMAactive sites in protic solvent (methanol).2. Immobilization of phosphomolybdic acid on imidazolium-basedmesoporous organosilicas for catalytic olefin epoxidationThe periodic mesoporous organosilicas containing different imidazoliumcations contents (PMO-ILs, a and b) were chosen as supports for the electrostaticimmobilization of12-phosphomolybdic acid (PMA). The resulting hybrid materials(PMA@PMO-ILs,2a and2b) were characterized by a variety of techniques. Theresults illustrated that PMA was successfully anchored on the surface and in thechannels of the PMO-ILs via electrostatic interaction and the structure of both thePMO-IL supports and the PMA were retained during the preparation processes.The catalytic properties of these materials (2a and2b) were investigated for theliquid-phase epoxidation of cyclooctene, and found that they were active with nearly100%selectivity to cyclooctene epoxide using TBHP as the oxidant. Furthermore,these hybrid catalysts could be reused several times without obvious loss of activityor selectivity under identical reaction conditions. Through comparative studies witha PMA-functionalized SBA-15material (2c), it suggested that the presence of theimidazolium cations in the framework of PMO-ILs should play key role instabilizing the catalytic active units against leaching during the reaction process. Therole of imidazolium cations could be further confirmed by studying anotherPMA-based catalyst (2d), which was obtained by anchoring PMA species on aminofunctionalized PMO-IL support. The catalytic activity and stability of2d decreasedslightly owning to the introduction of amino groups, which might prevent the PMAanions from interacting with the imidazolium cations in PMO-IL support. Based onthe above results, it can be conclude that an appropriate interaction between thePOM units and the supports should be established, and the supports should possess arationally high specific surface area and large pore size in order to fabricate highly efficient and stable POM-based heterogeneous catalysts.3. Immobilization of transition-metal-substituted phosphomolybdate onimidazolium-based mesoporous organosilica for catalytic olefin epoxidationThrough the electrostatic immobilization of transition-metal-substitutedphosphomolybdate (TMSP) onto PMO-IL (a), a series of suppored catalysts wereobtained. The resulting hybrid materials, including PCoMo11@PMO-IL (3a),PMnMo11@PMO-IL (4a), PNiMo11@PMO-IL (5), PCuMo11@PMO-IL (6a) werecharacterized by means of ICP-AES, N2adsorption-desorption, powder XRD, FT-IR,UV-Vis, and XPS. Characterizations indicated that TMSP were successfullyimmobilized on the surface and in the channels of PMO-IL and the structuralintegrity of PMO-IL and TMSP was remained throughout the preparation processes.The catalytic properties of these catalysts were evaluated for the epoxidation ofolefins using molecular oxygen as oxidant in combination with a co-reductantisobutyraldehyde. It was found that these functionalized materials showed goodactivity in the epoxidation of a wide range of olefins (including terminal ones).Under test conditions,3a exhibited the highest activity and selectivity to epoxides.In addition, the influence of different reaction parameters (such as temperature,time, the molar ratio of isobutyraldehyde to olefin, and oxidants) on the catalyticproperty of3a has also been studied. Based on the related publications andexperimental results, a possible reaction mechanism for the epoxidation of olefinswith molecular oxygen in the presence of isobutyraldehyde over these TMSPfunctionalized catalysts was proposed. The first stage is the generation of an acylradical through the reaction between the aldehyde and the transition metal site of theTMSP. The acyl radical in turn react with dioxygen to produce acyl peroxy radical,which have several pathways to achieve the selective oxidation of olefins. In short,the types and valence states of transition metal species in the supported catalystscould impact the oxidation rate and selectivity towards epoxides. The relatively high catalytic activity and selectivity of3a might be assigned to the presence of CoIIwithrelatively high electropositivity.更多还原