【作者】 吴长江；

【导师】 田琦峰；

【作者基本信息】 武汉工程大学 ， 化学工艺， 2019， 硕士

【摘要】 碳酸二苯酯（Diphenyl carbonate,简称DPC）作为制备工程热性塑料聚碳酸酯（PC）的重要中间体,其主要的合成方法有光气法,酯交换法和苯酚氧化羰基化法三种。其中,光气法的原料光气有剧毒,对人体和环境危害大;酯交换法的转化率低,能耗高,工艺复杂;而氧化羰基化法工艺简单,使用的原料价格低廉,无污染,因此更具有发展前途。对于苯酚氧化羰基化法来说,开发出高活性,高寿命和高选择性的高性能催化剂是目前研究的重点。负载型贵金属催化剂制备方式简单,使用后易于从反应体系中分离回收,以重复使用,因此可以节约大量的成本,符合目前绿色化学的发展趋势。对于高负载量的贵金属催化剂而言,在催化反应过程中只有极少数金属活性组分具有催化作用,因此催化剂中活性组分的尺寸大小对催化剂性能有着重要影响。一般而言,负载型的贵金属纳米颗粒的催化活性随着颗粒尺寸的减小而增强,这种现象被称为贵金属纳米催化剂的“尺寸效应”,其高活性归因于充当活性组分的贵金属在高比表面积的载体上以高分散纳米团簇的形式存在,可以充分利用催化活性位点。目前制备催化剂的方法:共沉淀法,沉积沉淀法,化学气相沉积法,浸渍法,微波辅助合成法和光沉积法等均已被用于纳米尺度催化剂的合成,其中光沉积法和微波辅助合成法作为高效的绿色环保新方法,在制备纳米尺度催化剂方面的应用得到广泛的拓展。本文重点研究了光沉积法和微波辅助合成法制备的纳米催化剂,并探讨了它们分别在苯酚氧化羰基化合成碳酸二苯酯反应中的催化性能,并通过XRD、TEM、XPS、H₂-TPR等测试对催化剂进行表征说明。本文主要研究内容如下:1.以锰氧化物八面体分子筛OMS-2为载体,采用光沉积法制备了一系列的负载型Pd/OMS-2催化剂,并与传统沉淀法和浸渍法制备的催化剂相比较,考察了它们分别在苯酚氧化羰基化反应中的催化性能。当Pd的负载量固定在2.5 wt%时,光沉积法制备的催化剂无论是在寿命还是稳定性上,都比传统的沉淀法和浸渍法制备的催化剂要优异:在连续反应24小时后DPC的收率可达到20.4%,并且在24小时后未出现明显的活性衰减现象。光沉积法制备Pd/OMS-2催化剂的机理如下:在紫外光照射下,OMS-2纳米棒会吸收光子而变成激发态,产生电子（e^-）—空穴对（h⁺）,其中空穴（h⁺）充当氧化剂,将溶液中的部分乙二醇氧化成成乙二醇自由基-OCH₂CH₂O·,从而促进Pd Cl中Cl^-的去除。而Pd²⁺将产生的电子（e^-）捕获,由此被还原成Pd⁰,剩余部分的乙二醇充当分散剂,阻止Pd颗粒的聚集。还原后的Pd粒子通过与载体OMS-2结合,形成更多的Pd-O键,使得催化剂即使在焙烧后,活性组分Pd粒子仍然保持高度分散的规整状态,而催化剂表面残留的乙二醇在高温焙烧后被除去。2.采用光沉积法制备催化剂时,对不同负载量及前驱体溶液不同p H值时制备的催化剂性能分别进行了考察,结果表明:采用光沉积法时,无论负载量为2.5 wt%还是5.0 wt%,制备的催化剂中活性组分Pd颗粒都分散良好,不同的是,当负载量超过2.5 wt%时,Pd颗粒的尺寸开始增大,在5.0 wt%时,Pd颗粒粒径达到3.48 nm,催化剂的催化活性也略微降低。在p H值为5时制备的催化剂,反应4小时后DPC收率可达到18.1%。3.以锰氧化物八面体分子筛OMS-2为载体,乙二醇为还原剂,采用微波辅助还原法和液相沉积还原法制备了不同的Pd/OMS-2催化剂,并考察其在苯酚氧化羰基化反应体系中的催化性能。采用液相沉积法制备催化剂时,传热不能同步进行,导致受热不均匀,Pd颗粒开始团聚。而微波法制备催化剂时,产生的电磁能量直接转换为热能,可在分子水平上产生热能,从而提供均匀的热量,因此微波加热会减少催化剂的结焦现象,并增强催化剂的稳定性。采用微波辅助法制备出来的催化剂,Pd颗粒尺寸小,分散度高,在催化苯酚氧化羰基化反应24小时后DPC的收率可达到16.1%。4.采用微波辅助合成法制备催化剂时,通过对前驱体溶液p H值的调控,达到优化催化剂性能的目的。结果表明:随着前驱体溶液p H值的增大,溶液中OH^-浓度逐渐增大,OH^-随后与乙二醇分解氧化后产生的乙醛共同作用下,对Pd Cl进行还原,并对还原后的Pd颗粒起到稳固作用。p H值为6时,制备的催化剂中Pd颗粒的主要粒径为2.56 nm,在用于催化苯酚氧化羰基化反应4小时后DPC的收率达到14.5%,此时催化剂性能达到最优。更多还原

【Abstract】 Diphenyl carbonate（DPC）is an important intermediate for the preparation of engineering thermal plastic polycarbonate（PC）.The main synthetic methods of DPC include phosgene,transesterification and phenol oxidative carbonylation.Among them,the raw material of phosgene method is highly toxic,which is harmful to human body and environment;the low conversion rate,the high energy consumption and the complex technique of the trasesterification method,lead to the inapplicability of the production;there are many advantages of oxidative carbonylation,including the cheap raw materials and pollution-free;therefore,it has a more promising future.For the phenol oxidative carbonylation process,it is essential to develop catalysts with high activity,long life and high selectivity.In generally,the preparation method of supported noble metal catalyst is simple;also,it is easy to separate and recover from the reaction system,so as to facilitate reuse,reduced the cost greatly as well and conforms to the development trend of green chemistry.For noble metal catalysts with high loads,only a few active components play a catalytic role in the process of catalytic reaction;therefore,the size of active component has an important influence on the catalytic performance.Generally speaking,the catalytic performance of supported catalyst increases with the decrease of size,which is called the noble metal nanocatalysts,and its good activity is attributed to the highly dispersed of noble metal,so that the catalytically active sites can be fully utilized.At present,the main methods,such as co-precipitation,chemical vapor deposition,impregnation,microwave-assisted synthesis and photo-deposition methods have been already used to synthesize nano-catalysts on metal oxides.Among them,microwave-assisted and photo-deposition methods,as efficient green environmental protection new technologies,which have been widely used in the preparation of catalysts.In this paper,the catalytic performance of catalysts prepared by microwave-assisted and photo-deposition methods were discussed,and the catalysts were characterized by XRD,TEM,XPS,and H₂-TPR.The main contents of this paper are as follows:（1）The manganese oxide octahedral molecular sieve（OMS-2）was used,and a series of supported Pd/OMS-2 catalysts were prepared by photo-deposition method（Pd/OMS-2-PD）,compared with the catalysts prepared by traditional precipitation（Pd/OMS-2-Pre）and impregnation methods（Pd/OMS-2-IM）,their properties in the oxidative carbonylation of phenol were investigated.The catalyst prepared by photo-deposition method showed a better catalytic performance than other two catalysts,which were prepared by the traditional methods.Among them,the yield of DPC could reach 20.4%at 24 hours by using Pd/OMS-2-PD,and there was no obvious decay of activity.The possible mechanism of photo-deposition was as follows:OMS-2 nanorods become excited states under ultraviolet irradiation,electrons（e^-）-hole pairs（h⁺）were produced,in which holes（h⁺）acted as oxidants,converted part of ethylene glycol into ethylene glycol free radical-OCH₂CH₂O·and promotes the removal of Cl^-in Pd Cl.The generated electrons（e^-）was captured by Pd²⁺,and then,Pd²⁺reduced to Pd⁰.The remained ethylene glycol acted as a dispersant to prevent the agglomeration of Pd particles.More Pd-O bonds were formed after Pd combined with OMS-2,which makes the active component Pd particles remain highly dispersity,even after calcination,and the residual glycol on the catalyst surface was removed after calcination at high temperature.（2）The performance of the catalysts prepared by photo-deposition method under different loadings and different p H condition were investigated.The results showed that the active component Pd particles were highly dispersed,no matter the loading amount is2.5 wt%or 5.0 wt%.,the particle size of Pd gradually increases when the load exceeded2.5 wt%,at 5.0 wt%,the particle diameter of Pd particles reached 3.48 nm and the catalytic activity also slightly decreased.The DPC yield reached 18.1%when the p H value was at 5.（3）A series of Pd/OMS-2 catalysts were prepared by microwave-assisted reduction（MW-Pd/OMS-2）and liquid-phase deposition reduction（LR-Pd/OMS-2）methods,with manganese oxide octahedral molecular sieve OMS-2 as support and ethylene glycol as reductant and their catalytic performance in phenol oxidative carbonylation were investigated.The heat transfer cannot be out simultaneously and not uniform when the catalyst was prepared by liquid phase deposition.The heat energy is directly converted by electromagnetic energy,to transfer the heat evenly when the catalyst was prepared by the microwave-assisted method and the Pd particle size was small and highly dispersity.（4）The catalytic performance prepared by microwave-assisted method was optimized by adjusting the p H of the precursor solution.With the increased of p H value,the concentration of OH^-gradually increased,and the Pd Cl was reduced and stabilized by the interaction of OH^-and acetaldehyde.The catalytic performance is optimal at p H=6,and the main particle size of Pd is 2.56 nm,the yield of DPC reached14.5%after catalyzing phenol oxidative carbonylation.更多还原