本文關(guān)鍵詞：CeO_2納米管負(fù)載Pd催化苯酚氧化羰基化反應(yīng)　出處：《河北工業(yè)大學(xué)》2015年碩士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 碳酸二苯酯 氧化羰基化 鈀催化劑 氧化鈰納米管 易還原氧物種

【摘要】：近年來,由于工程塑料聚碳酸酯的廣泛應(yīng)用,對其原料碳酸二苯酯(DPC)的需求大增,使得DPC的合成研究成為人們關(guān)注的熱點(diǎn)。苯酚氧化羰基化反應(yīng)合成DPC是一條“綠色”的工藝路線,原料低毒、無污染、價格便宜,工藝流程簡單,非常具有發(fā)展?jié)摿�。苯酚氧化羰基化反�?yīng)是一個多步電子轉(zhuǎn)移催化體系,通常使用Pd及其化合物作為催化劑,同時加入各種助劑來提高催化性能;Ce化合物即為一種有效的助劑。CeO_2是工業(yè)催化中最具意義的稀土氧化物,擁有氧化還原離子對(Ce3+/Ce4+),Ce4+和Ce3+之間可以實(shí)現(xiàn)快速可逆的氧化還原循環(huán),在多相催化中有廣泛的應(yīng)用前景。本文以多壁碳納米管為硬模板,乙醇為分散劑,Ce(NO3)3·6H2O為Ce前體,通過液相沉積-水熱法制備出一維管狀納米氧化鈰(CeO_2-NT)。利用TEM、SAED、XRD、N2等溫吸附-脫附、H2-TPR、CO-TPD、Raman、XPS等對其結(jié)構(gòu)性質(zhì)進(jìn)行了表征,所得CeO_2-NT外徑~25 nm,長度大于300 nm,管壁由粒徑4~9 nm的CeO_2晶粒組成,比表面積為108.8 m2/g。相對于采用微乳液法制備的零維顆粒CeO_2-P,CeO_2-NT表面存在較多的氧空位,更容易活化分子氧,產(chǎn)生了較多的易還原吸附氧物種。分別以CeO_2-NT和CeO_2-P為載體,采用原位方法制備了Pd-O/CeO_2-NT和Pd-O/CeO_2-P催化劑。用于催化苯酚氧化羰基化反應(yīng),Pd-O/CeO_2-NT催化反應(yīng)活性和DPC選擇性均高于后者。通過表征發(fā)現(xiàn),在Pd-O/CeO_2-NT催化劑中,CeO_2表面氧活性、密度均有所增加,因而使用其作為催化劑,苯酚轉(zhuǎn)化率較高。同時,由于Pd被高度分散到載體表面,并部分進(jìn)入CeO_2晶格,形成固溶體。Pd與CeO_2之間存在著強(qiáng)相互作用,更加有利于Pd、Ce之間的電子轉(zhuǎn)移。反應(yīng)中被還原的Pd(0)可以容易地向Ce(IV)轉(zhuǎn)移電子,重新被氧化為Pd(II),恢復(fù)生成DPC的能力,從而具有較高的選擇性。對Pd-O/CeO_2-NT催化苯酚氧化羰基化反應(yīng)進(jìn)行了條件優(yōu)化,當(dāng)CO壓力為6.6MPa,催化劑量為Pd/Phenol=1/425(摩爾比)時,在110°C反應(yīng)7 h,苯酚轉(zhuǎn)化率為67.7%,DPC選擇性為93.3%。該催化劑的重復(fù)使用性能較差,第二次使用時,苯酚轉(zhuǎn)化率為29.3%,DPC選擇性為62.3%。這是由于Pd-O/CeO_2-NT的管狀結(jié)構(gòu)在反應(yīng)過程中被破壞,易還原氧物種消失,并且活性組分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.
【學(xué)位授予單位】：河北工業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：O621.251

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