【作者】 王哲；

【导师】 许宪祝； 林凯峰；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2021， 博士

【摘要】 烷基苯的直接氧化产物醇、醛、酮及酸是工业上重要化学品的中间体,在工业上和实验室都具有重要的价值。早期使用一些强氧化剂进行烷基苯的氧化反应存在腐蚀性强、高毒性、选择性差、不经济和处理困难等诸多问题。为了满足生产和生活上可持续发展的需要,基于宏观三维大孔树脂的无模板法开发多种环境友好、高稳定性、低成本、高选择性又可重复使用的介孔碳基材料用来催化乙苯到苯乙酮反应是本论文研究重点。主要包括以下三个部分:第一部分利用草酸高铁酸根离子交换的IRA-900大孔树脂通过一步热解制备了一系列宏观三维Fe₃C/Fe/C复合材料CIPC-T（T表示热解温度）。CIPC-T材料中三维介-大孔无定形碳骨架内部嵌入了大量高度分散的纳米颗粒,这些纳米颗粒具有Fe₃C/Fe表面包覆着石墨壳层（CI@GC）的核壳结构。根据XRD、SEM、TEM、TGA及定量相分析的结果,提出了复合材料的形成过程同时也确定了材料中Fe₃C与Fe的含量。CIPC-T中Fe₃C/Fe的质量比可以通过热解温度很容易地调节,进而获得了不同饱和磁化强度的磁性材料。在叔丁基过氧化氢存在下CIPC-750催化剂能有效地将乙苯氧化成苯乙酮并表现出58.7%的转化率并且证实了Fe₃C在反应中的活性作用。球径为200～400μm的CIPC-T催化剂的宏观球形形貌和出色的磁学性能也有利于从反应溶液中分离和回收。此外,CIPC-T复合材料中铁位点的高稳定性是由于CI@GC的外石墨壳层保护使反应过程中不易发生铁物种的浸出,也使催化剂表现出很好的循环利用性。第二部分利用二氰二胺与IRA-900大孔树脂在不同比例下一步热解制备了一系列的三维尺寸为600～900μm的多级孔氮掺杂碳球x-DIRA-T（其中x表示二氰二胺与IRA-900的用量比和T表示热解温度）。二氰二胺作为一种氮掺杂剂和抗收缩剂的加入可以有效控制树脂在热解过程中的收缩,这有利于保留原始大孔树脂中的三维互联孔道和创造丰富的氮掺杂位点。这也有效地解决了第一部分有大孔树脂热解骨架收缩的问题。当二氰二胺与树脂比例达到1:1时催化剂可以高选择性的将乙苯转化为苯乙酮,显著超过了直接煅烧树脂表现的活性（乙苯转化率分别为83.5%和12.1%）。结构表征和反应动力学研究表明催化剂较大的孔体积和更多的介-大孔结构可以暴露更多的活性位点和较低的扩散限制,这能够明显加快初始反应速率从而提高催化性能。x-DIRA-T催化剂更大的宏观三维尺度可以更有效发挥反应中分离和回收的优势。这部分工作提出了一种在直接一步热解过程中保持碳有机前体孔隙尺度多样性的新策略,使其作为宏观三维载体能更有效地应用于多相催化领域。第三部分继续研究氮掺杂碳材料对乙苯氧化到苯乙酮活性的影响。根据第二部分二氰二胺与大孔树脂混合热解后二氰二胺残留的现象为启发,进一步讨论石墨相氮化碳及其前驱体与有机物共热解时热稳定性的问题。石墨相氮化碳（GCN）通常被认为是一种自牺牲的氮源,常常与多种有机化合物一起通过混合共热解过程获得氮掺杂碳材料。但通过热重分析、热重-质谱联用分析和X射线光电子能谱分析,我们发现含有丰富氢键的GCN可以不可逆地被各种有机物质释放出的碳质气体片段锚定,进一步促使氮化碳转化成氮掺杂石墨烯,表明GCN在与有机物供热解时不再在是一个自牺牲的氮源,而这些残留的氮化碳对整体氮掺杂碳材料的孔隙度和可接近活性中心数量都起到了关键作用。所以设计了一种CVD的策略,利用固体碳源AB-8树脂与基底物质GCN一步热解获得了超高介孔隙度和超薄形态的ABCNS-900催化剂,得益于催化剂优异的介孔结构,比表面积和孔容分别为1650 m² g^-1和8.26 cm³ g^-1,以低剂量就能高选择性将乙苯氧化为苯乙酮,表现了极好的催化活性,乙苯转化率和苯乙酮选择性分别达到99.8%和96.2%。我们的研究结果为高介孔体积的超薄氮掺杂石墨烯提供了一种绿色经济的合成策略,进一步促进了氮掺杂碳材料在多相催化工业中的应用。更多还原

【Abstract】 Alcohols,aldehydes,ketones and acids,which are directly oxidized products of alkylbenzenes,are intermediates of important industrial chemicals,and have important values in industry and laboratories.The early use of some metered-type strong oxidants for the oxidation of alkylbenzene has many problems such as strong corrosiveness,high toxicity,poor selectivity,uneconomical and difficult handling.In order to meet the needs of sustainable development in production and life,the template-free method based on macroscopic three-dimensional macroporous resins has developed a variety of environmentally friendly,high stability,low cost,high selectivity and reusable mesoporous carbon-based materials.Catalyzing the reaction of ethylbenzene to acetophenone is the focus of this thesis.It mainly includes the following three aspects:Part 1:A series of multi-scaled cementite/iron porous carbon（CIPC-T,T）composites with extremely low nitrogen content and millimeter-size spherical format are successfully prepared through a simple carbothermal pyrolysis of exchanged resin spheres by ferric oxalate anions.CIPC-T samples are characterized to be composted of highly dispersed core-shell structured Fe₃C/Fe@graphitic carbon（CI@GC）nanoparticles embedded in porous amorphous carbon frame.The mechanism for the formation of the composites is proposed based on the results of XRD,SEM,TEM and TGA.Interestingly,Fe₃C contents can be easily controlled just by different carbothermal temperatures.The CIPC-T samples prove to be active to catalyze oxidation of ethylbenzene to acetophenone as a heterogeneous catalyst（ethylbenzene conversation of 58.7%）.For the first time,the role of Fe₃C for the catalytic oxidation has been confirmed.Either the spherical format of the composites with 200～400μm or the magnetization property facilitates the separation of the catalyst from the reaction solution.More importantly,no leaching of iron active sites occurs during the reactions and the catalyst can be reusable in continuous runs without obvious loss of activity.Such high stability of iron sites in the composites is ascribed to the protection of the outer graphitic carbon shell of CI@GC.Part 2:A series of nitrogen doped 3D hierarchically porous carbon beads with size of 0.6～0.9 mm are successfully prepared by one-step pyrolysis of dicyandiamide and macroporous resin under different ratio.Dosage of dicyandiamide can effectively control shrinkage of resins during pyrolysis,and favor to create 3D interconnected pore channels and abundant nitrogen doped sites as a self-sacrificing dopant and activating-like agent.The beads display excellent conversion for ethylbenzene to acetophenone as opposed to only calcinating pristine IRA resins（83.5%vs 12.1%）,when the ratio reach 1:1.At initial reaction period,linear relationships between concentration of reactants and products are established to evaluate whether the beads are provided with diffusion limitation in mentioned reaction.Structural characterization and reaction kinetic studies indicate that the larger mesoporous pore volume and more meso/macro-pore structure of the beads can expose more accessible active sites and lower diffusion limitation,significantly affecting the initial rates,thereby improving the catalytic performance.In addition,macro-beads in size of millimeter scale can effectively exert the advantages of easy separation and recovery.A new strategy is provided which can keep the diversity of pore scale in porous carbonous precursors during pyrolysis,thereby more effectively applying in heterogeneous catalysis.Part 3:The third part continues to study the effect of nitrogen-doped carbon materials on the oxidation of ethylbenzene to acetophenone.According to the second part of the phenomenon of dicyandiamide residue after pyrolysis of the mixed pyrolysis of dicyandiamide and macroporous resin,the problem of thermal stability during the co-pyrolysis of graphite phase carbon nitride and its precursors and organic matter is further discussed.Traditionally,graphitic carbon nitride（GCN）is commonly considered as a self-sacrificed nitrogen source together with multifarious organic compounds to obtain N doped carbon materials by a co-pyrolysis process.However,through TGA,TGA-MS and XPS,we found that GCN,which was rich in hydrogen bonds,can be irreversibly anchored by thermal decomposition products from various organic substances,further promoting GCN into N doped graphene.Therefore we present a chemical vapor deposition（CVD）strategy for preparing a series of ultrathin N doped graphene with highly mesoporous(1650 m² g^-1and 8.26 cm³g^-1).Benefitting from the outstanding mesoporosity and ultrathin morphology,the representative ABCNS-900 exhibits excellent catalytic performance for oxidizing ethylbenzene to acetophenone with extremely low dosage and high selectivity（96.2%）.Our findings show a universal synthetic strategy for ultrathin N-rich carbon nanosheets with high mesopore volume,further promoting the application of N doped carbon materials in heterogeneous catalytic industry.更多还原