【作者】 李超；

【导师】 程铁欣； 周广栋；

【作者基本信息】 吉林大学 ， 物理化学， 2012， 博士

【摘要】 乙烷氧氯化脱氯化氢制备氯乙烯是一种新型工艺，该工艺比传统氯乙烯生产方法更经济，高效。本文制备了镁铝复合氧化物和TiO₂载体负载的CuCl₂基催化剂，以及稀土元素（La﹑Ce）改性的CuCl₂基催化剂。通过各种表征手段对催化剂的结构，氧化还原性质，表面酸性，活性组分的存在状态，以及活性组分与助剂之间的相互作用进行了系统的分析。考察了稀土助剂对乙烷氧氯化脱氯化氢制氯乙烯反应性能的影响，对催化活性中心与稀土元素（La﹑Ce）之间的作用机理进行了进一步的探讨。系统地考察了CeO₂分散状态对CuCl₂基催化剂的物理化学性质和乙烷氧氯化脱氯化氢制氯乙烯反应活性的影响。在反应温度T=500℃，空速GHSV＝₃200h^-1，流量比V_C2H6/V_HCl/V_air=1/2/5条件下，晶化的CeO₂物种显著提高了乙烷转化率和氯乙烯的选择性，归因于助剂CeO₂表面存在大量的空穴氧物种（O^-，O₂^-），加速了氧化还原对(Cu⁺/Cu²⁺)的转化，提高了催化反应活性。考察了第二助剂La₂O₃的引入，对CuCl₂基催化剂物理化学性质的影响，研究发现：助剂La₂O₃前驱体溶液的浸渍顺序和La含量对活性物种CuCl₂的存在状态影响显著；载体先浸渍La₂O₃先驱体溶液，促进了活性物种CuCl₂沉降在载体表面；其中，CuCl₂基催化剂中La含量在3wt.%时，表面氯化铜含量最多，显著地提高了乙烯和氯乙烯的总选择性，而La含量在5wt.%时，活性物种CuCl₂与CeO₂协同作用最佳，对氯乙烯选择性的提高有利。采用水热合成法成功了制备了TiO₂载体和杂原子La，Ce，Zr改性的TiO₂载体。实验结果表明：杂原子La，Ce，Zr的引入对TiO₂载体的结构影响较大。其中，Ce³⁺改性的TiO₂载体，表面形成了较多的弱酸中心，更有利于烷基氯化物脱除氯化氢反应的进行；同时，CuCl₂-KCl/Ce-TiO₂催化剂上的活性物种Cu²⁺更容易还原，提高了Cl₂的生成速率，对乙烷的氯化反应和乙烯与氯气加成反应有利；此外，纯TiO₂和杂原子改性TiO₂载体负载的CuCl₂基催化剂上，铜离子存在两种状态，Cu²⁺和Cu⁺。更多还原

【Abstract】 Vinyl chloride monomer （VCM） is an important monomer in the manufactureof polyvinyl chloride （PVC）. Nowadays, VCM is commercially produced by threeprocesses: acetylene process, ethylene oxychlorination and ethane oxychlorination.We often select mercuric chloride as a main catalyst to produce vinyl chloride inprocess of acetylene oxychlorination. The method is easy to ultilize due to its simpleand mature, but it brings some disadvantage including high energy consumption andserious pollution to environment.Ethylene oxychlorination is main route to produce vinyl chloride. This processincludes two reactions: the process of manufacture of ethane chlorides and thecracking of ethylene dichloride （EDC）. This method is advantageous to theimprovement of quality of products, but the technics is complex to produce vinylchloride. In addition, its cost fluctuates along with the change of price of oil.The oxychlorination reaction of ethane is a promising and economic route toproduce vinyl chloride, because ethane as a raw material is cheaper than ethylene.Europe Vinyl Corporation succeeds to set up two equipments at the Bay of Mexicoin1999s, and make it come true in2003s. The total capacity of production of vinylchloride reaches up0.3million ton per year. By contrast, there is no report about thistechnique in our county. Therefore, study of preparation of vinyl chloride by ethaneoxychlorination is of great importance.In this work, copper-base catalysts modified with other components wereprepared by conventional impregnation method, and the catalytic activity for ethaneoxychlorination reaction was investigated simultaneously. The catalysts werecharacterized by means of XRD, BET, H₂-TPR, SEM, TEM, UV-Vis and XPS etc. toinvestigate the relationship between the structure, surface acidity, redox properties,existence state of components and the catalytic performance. The main experimentalresults and conclusion are as follows:1. Oxychlorination of ethane over CeO₂modified CuCl₂-KCl/MgO^-Al₂O₃catalystCeO₂modified CuCl₂-KCl/MgO^-γ-Al₂O₃catalysts were prepared by an impregnation method, and the influence of Cerium content on the structure, redox,acidity and existence state of active components was investigated. It is found thatthree types Cerium species exist on the surface of catalysts: dispersed ceria, smallaggregated crystalline ceria species and large ceria particles.XRD, BET and H₂-TPR tests indicated that ceria is highly dispersed on thesupport at cerium content x <1.4wt.%, and large ceria particles begin to form on thesurface of catalysts at cerium loading x≥9wt.%; while for catalysts with ceriumcontent1.4wt%≤x <9wt%is responsible for the formation of small aggregatedcrystalline ceria species on the catalysts.Cerium promoter plays a key role for the formation of weak acid center on thesurface of catalysts. CeO₂-CuCl₂-KCl/MgO^-γ-Al₂O₃catalysts exhibit mainly Lewisacid center, and the amount of weak acid sites reach a maximum for catalyst withcerium content x=5wt%. It is known that weak acid center is advantageous tode-hydrochloric from ethane dichloride, which is responsible for the improvement ofselectivity of ethylene and vinyl chloride.CuCl₂-based catalysts with small aggregated crystalline ceria possess largeamount of surface capping oxygen species （O^-, O₂^-） on the surface and reach amaximum with cerium content x=5wt%. As a result, Cu⁺species is hardlyreduced to Cu⁰, which is responsible for the high stability of CuCl₂-based catalyst.The experiment results show that both ethane conversion and selectivity ofvinyl chloride reach a maximum （98.6%and54.6%） for CuCl₂-based catalyst withcerium content x=5wt%, while the selectivity of ethylene reach a minimum（₂6.₂%） simultaneously. Additionally, the best reaction condition is that: T=500℃，GHSV＝₃₂00h-1and VC₂H6/VHCl/Vair=1/₂/5.2. Oxychlorination of ethane over CeO₂/La₂O₃bi-promoter modifiedCuCl₂-KCl/MgO^-Al₂O₃catalystCeO₂/La₂O₃bi-promoter modified CuCl₂-KCl/MgO^-Al₂O₃catalysts wereprepared by conventional impregnation method. The experiment results show thatimpregnation order of La₂O₃precursor can affect the structure, redox, acidity andexistence state of active component of CuCl₂-based catalyst notably.MgO^-γ-Al₂O₃support impregnated with La₂O₃precursor firstly improves thedispersion capacity of CeO₂and KCl promoters on the support. In addition, itbenefits the deposition of active CuCl₂species on the surface of support. As a result, the conversion of Cu⁺to Cu²⁺is accelerated and more active Cu²⁺can participate inthe reaction, which is responsible for the high activity of ethane oxychlorination.Lanthanum content can affect the acidity of CuCl₂-based catalysts notably. Afew amount of La species benefit the formation of weak acidic centers, which isattributed to the coverage of uncovered Al³⁺by La³⁺species. By contrast, largeamount of La promoter is responsible for the decrease of acidic amount, which isattributed to the big radius of La³⁺ion and the decrease of interaction between La³⁺and OH-species.La₂O₃promoter improves the stability of Ce-Cu/Laxcatalysts notably, whichis attributed to the higher ability of prohibiting the coke species deposited on thesurface. After reaction for180hours, conversion of ethane and selectivity of vinylchloride is97%and₃8.₂%, respectively; and the selectivity of ethylene is44%,simultaneously.TEM images show that coke species deposited on the Ce-Cu/La₃are easilyeliminated and form large amount of circle coke layer on the edge of used catalyst,which is responsible for the high stability of CuCl₂-based catalysts.₃. Study of ethane oxychlorination over CuCl₂catalysts supported on La, Ce,Zr atoms modified TiO₂supportPure TiO₂and La, Ce, Zr atoms modified TiO₂support were prepared usinghydrothermal treatment method. It is found that the introduction of La, Ce and Zratom to TiO₂support plays a key role for the formation of physico-chemicalproperties of support.The surface area of La, Ce, Zr atoms modified TiO₂increases apparentlycompared to pure TiO₂support; and these atoms exist in the different position ofTiO₂support. Zr⁴⁺can insert in to Ti⁴⁺lattice or interstitially position of TiO₂due tothe closer radius; while La³⁺or Ce³⁺ion can insert into interstitially position or existon the surface of TiO₂attributed to the bigger radius.The introduction of La, Ce and Zr atom to TiO₂support affects the acidity ofsupport notably. It is worth to point out that Ce³⁺ion benefits the formation of weakacidic center; and both weak and middle acidic amount increase for La³⁺modifiedTiO₂support. By contrast, the amount of middle acidic center increases apparently onZr^4-ions modified TiO₂support.H₂-TPR tests show that the reduction temperature of active Cu²⁺species decreases with an order of CuK/TiO₂<CuK/La-TiO₂<CuK/Ce-TiO₂≈CuK/Zr-TiO₂.This fact suggests that higher dispersion of active component benefits the reductionof active copper species on the support. However, Ce-TiO₂support displays thelower surface area, which suggests the strong interaction existed between activeCu₂+and Ce₃+species. As a result, more Cl₂intermediate can be formed during thereaction, which is advantageous to the conversion of ethane and selectivity of vinylchloride.XPS results show that both Cu⁺and Cu²⁺ions exist on the surface ofCuCl₂-based catalyst, simultaneously. Additionally, Ce-TiO₂support exhibits thestronger electro-negativity compared to other support, which is advantageous to thereduction of Cu²⁺to Cu+and is responsible for the excellent activity.更多还原