CeO_2纳米管负载Pd催化苯酚氧化羰基化反应

发布时间：2017-12-26 18:26

本文关键词：CeO_2纳米管负载Pd催化苯酚氧化羰基化反应　出处：《河北工业大学》2015年硕士论文　论文类型：学位论文

【摘要】：近年来,由于工程塑料聚碳酸酯的广泛应用,对其原料碳酸二苯酯(DPC)的需求大增,使得DPC的合成研究成为人们关注的热点。苯酚氧化羰基化反应合成DPC是一条“绿色”的工艺路线,原料低毒、无污染、价格便宜,工艺流程简单,非常具有发展潜力。苯酚氧化羰基化反应是一个多步电子转移催化体系,通常使用Pd及其化合物作为催化剂,同时加入各种助剂来提高催化性能;Ce化合物即为一种有效的助剂。CeO_2是工业催化中最具意义的稀土氧化物,拥有氧化还原离子对(Ce3+/Ce4+),Ce4+和Ce3+之间可以实现快速可逆的氧化还原循环,在多相催化中有广泛的应用前景。本文以多壁碳纳米管为硬模板,乙醇为分散剂,Ce(NO3)3·6H2O为Ce前体,通过液相沉积-水热法制备出一维管状纳米氧化铈(CeO_2-NT)。利用TEM、SAED、XRD、N2等温吸附-脱附、H2-TPR、CO-TPD、Raman、XPS等对其结构性质进行了表征,所得CeO_2-NT外径~25 nm,长度大于300 nm,管壁由粒径4~9 nm的CeO_2晶粒组成,比表面积为108.8 m2/g。相对于采用微乳液法制备的零维颗粒CeO_2-P,CeO_2-NT表面存在较多的氧空位,更容易活化分子氧,产生了较多的易还原吸附氧物种。分别以CeO_2-NT和CeO_2-P为载体,采用原位方法制备了Pd-O/CeO_2-NT和Pd-O/CeO_2-P催化剂。用于催化苯酚氧化羰基化反应,Pd-O/CeO_2-NT催化反应活性和DPC选择性均高于后者。通过表征发现,在Pd-O/CeO_2-NT催化剂中,CeO_2表面氧活性、密度均有所增加,因而使用其作为催化剂,苯酚转化率较高。同时,由于Pd被高度分散到载体表面,并部分进入CeO_2晶格,形成固溶体。Pd与CeO_2之间存在着强相互作用,更加有利于Pd、Ce之间的电子转移。反应中被还原的Pd(0)可以容易地向Ce(IV)转移电子,重新被氧化为Pd(II),恢复生成DPC的能力,从而具有较高的选择性。对Pd-O/CeO_2-NT催化苯酚氧化羰基化反应进行了条件优化,当CO压力为6.6MPa,催化剂量为Pd/Phenol=1/425(摩尔比)时,在110°C反应7 h,苯酚转化率为67.7%,DPC选择性为93.3%。该催化剂的重复使用性能较差,第二次使用时,苯酚转化率为29.3%,DPC选择性为62.3%。这是由于Pd-O/CeO_2-NT的管状结构在反应过程中被破坏,易还原氧物种消失,并且活性组分Pd流失所致。
[Abstract]:In recent years, due to the extensive application of engineering plastics polycarbonate, the demand for two phenyl carbonate (DPC) of raw materials has increased greatly, making the research of DPC synthesis become the focus of attention. The oxidative carbonylation of phenol to DPC is a "green" process. The raw material is low toxic, pollution-free and cheap, and the process is simple and has great potential for development. Oxidative carbonylation of phenol is a multi-step electron transfer catalyst system. Usually Pd and its compounds are used as catalysts, and various auxiliaries are added to improve catalytic performance. Ce compounds are effective additives. CeO_2 is the most significant rare-earth oxide in industrial catalysis. It has fast redox cycle between Ce3+/Ce4+ and Ce4+ and Ce3+, and has wide application prospects in heterogeneous catalysis. In this paper, multi walled carbon nanotubes (CNTs) as hard template, ethanol as dispersant, Ce (NO3) 3? 6H2O as Ce precursor, one dimensional tubular nanosized cerium oxide (CeO_2-NT) was prepared by liquid phase deposition hydrothermal method. The structure and properties of TEM, SAED, XRD and N2 were characterized by isothermal adsorption desorption, H2-TPR, CO-TPD, Raman and XPS. The CeO_2-NT outer diameter was ~25 nm, and the length was more than 300. The wall of the tube was composed of grain size and grain size, and the specific surface area was 108.8. Compared with the zero dimension particle CeO_2-P prepared by microemulsion method, there are more oxygen vacancies on the surface of CeO_2-NT, which are easier to activate molecular oxygen and produce more easily reductive and adsorptive oxygen species. Pd-O/CeO_2-NT and Pd-O/CeO_2-P catalysts were prepared by in situ method with CeO_2-NT and CeO_2-P as the carrier, respectively. The catalytic activity of Pd-O/CeO_2-NT and the selectivity of DPC are higher than that of the latter for the oxidation carbonylation of phenol. It was found that the oxygen activity and density of the surface of CeO_2 increased in the Pd-O/CeO_2-NT catalyst, so the conversion rate of phenol was higher by using it as a catalyst. At the same time, Pd is highly dispersed to the surface of the carrier and partially into the CeO_2 lattice, forming a solid solution. There is a strong interaction between Pd and CeO_2, which is more beneficial to the electron transfer between Pd and Ce. The reduced Pd (0) can easily transfer electrons to Ce (IV), reoxidize to Pd (II), restore the ability to generate DPC, and thus have high selectivity. The conditions for optimizing the oxidative carbonylation of phenol catalyzed by Pd-O/CeO_2-NT were optimized. When the CO pressure is 6.6MPa and the catalyst amount is Pd/Phenol=1/425 (mole ratio), the reaction rate is 67.7% h at 110 degree C, and the selectivity of DPC is 93.3%. The reusable performance of the catalyst is poor. The conversion rate of phenol is 29.3% and the selectivity of DPC is 62.3% when used for second times. This is due to the destruction of the tubular structure of Pd-O/CeO_2-NT in the reaction process, the disappearance of the reductive oxygen species and the loss of the active component Pd.
【学位授予单位】：河北工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：O621.251

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