1、硕 士 学 位 论 文氯掺杂 Ba0.5Sr0.5Co0.8Fe0.2O3-透氧性能及其用于低碳烷烃转化Oxygen Permeability of Chlorine Doped Ba0.5Sr0.5Co0.8Fe0.2O3- and Their Applications in Low Carbons Alkanes ConversionA Dissertation Submitted for the Degree of MasterCandidate：Liu HongfeiSupervisor：Prof. Wang HaihuiSouth China University of Techno
2、logy Guangzhou, China华南理工大学学位论文原创性声明本人郑重声明：所呈交的论文是本人在导师的指导下独立进行研究所取得的研究成果。除了文中特别加以标注引用的内容外，本论文不包含任何其他个人或集体已经发表或撰写的成果作品。对本文的研究做出重要贡献的个人和集体，均已在文中以明确方式标明。本人完全意识到本声明的法律后果由本人承担。作者签名： 日期： 年 月 日学位论文版权使用授权书本学位论文作者完全了解学校有关保留、使用学位论文的规定，即：研究生在校攻读学位期间论文工作的知识产权单位属华南理工大学。学校有权保存并向国家有关部门或机构送交论文的复印件和电子版，允许学位论文被查阅（除在
3、保密期内的保密论文外）；学校可以公布学位论文的全部或部分内容，可以允许采用影印、缩印或其它复制手段保存、汇编学位论文。本人电子文档的内容和纸质论文的内容相一致。本学位论文属于：保密，在 年解密后适用本授权书。不保密，同意在校园网上发布，供校内师生和与学校有共享协议的单位浏览。(请在以上相应方框内打“”)作者签名： 日期：指导教师签名： 日期：作者联系电话： 日期：联系地址（含邮编）： 电子邮箱：I摘 要钙钛矿型氧化物由于在催化，超导，气敏传感，固体氧化物燃料电池，铁电体及铁磁体等方面的广泛应用而受到了越来越多人的关注。此外，基于钙钛矿型氧化物的膜反应器在低碳烃选择性氧化工艺过程强化方面也展示巨
4、大的前景。然而目前为止，所报道的这些钙钛矿型氧化物由于在还原性型气氛下（低碳烷烃及其选择性氧化后的某些产物具有还原性）不稳定，催化活性不高，或者是在低碳烷烃反应温度下透氧量偏低而没能得到实际的应用。过去 20 多年里，在钙钛矿结构中的 A 位或者 B 位进行阳离子掺杂是开发新型钙钛矿透氧膜材料最主要手段，但还没有报道阴离子位掺杂的钙钛矿透氧膜材料。然而已有文献报道，对钙钛矿型氧化物进行阴离子位的卤族元素的掺杂可以改善钙钛矿型氧化物体系氧离子迁移速率，提高其选择性氧化催化活性。基于以上这些事实，本文首次研究了氯掺杂的钙钛矿型透氧膜材料的相关性能。本文以 Ba0.5Sr0.5Co0.8Fe0.2O
5、3- (BSCF)和 Ba0.5Sr0.5Co0.8Fe0.2O3-Cl0.04 (BSCFCl0.04)两个组成钙钛矿透氧膜材料的性能对比研究贯穿于始终，考查了氯掺杂对 BSCF 的透氧性能及其在低碳烃选择性氧化（甲烷氧化偶联、乙烷氧化脱氢）方面的催化性能的影响。X 射线衍射分析表明 BSCF 和 BSCFCl0.04 两个粉体均形成了完整的立方钙钛矿结构。X 射线光电子能谱揭示氯掺杂降低了金属氧键的结合能。氧程序升温脱附实验结果表明氯掺杂增大了 BSCF 在600900 oC 的储氧能力。首先，我们进行了低温透氧实验。在 575700 oC 的温度范围内，BSCFCl0.04 均展示了高于
6、 BSCF 的透氧量。在 600 oC 时，1 mm 厚的 BSCFCl0.04膜片的透氧量高达 0.29 mlmin-1cm-2，几乎是同样测试条件下 BSCF 透量的 3倍。这表明氯掺杂提高了 BSCF 材料的氧离子导电性，与通过 X 射线光电子能谱表征所得结论一致。另外，在 600 oC 下进行的长达 120 个小时的透氧稳定性测试过程中，BSCFCl 0.04 透氧量没有出现显著的衰减，这说明 BSCFCl0.04 材料具备优异的结构稳定性，远远好于文献报道的有关 BSCF 的稳定性。通过 X 射线衍射对透氧测试前后膜片的晶相结构进行分析，我们进一步证实这一点。基于钙钛矿透氧膜材料的膜
7、反应器由于能够实现低碳烃的选择性氧化与氧气分离的耦合而展示了相对于传统的低碳烃转化工艺明显的优势。然而这些钙II钛矿型膜材料存在着选择性氧化催化活性不高的缺点。有文献报道卤素掺杂是改进钙钛矿型氧化物材料的选择性氧化反应（如甲烷氧化偶联、乙烷脱氢等）催化活性的有效手段。因此，本文也研究了氯掺杂对 BSCF 的甲烷氧化偶联催化活性的影响。催化性能测试选择在固定床上进行。另外，笑气因为适合于选择性氧化反应而被用作氧源。在 850 oC 时，乙烷乙烯（C 2）收率达到最大值30.7%，此时对应的 CH4/N2O 进料摩尔比为 0.4，甲烷转化率为 66.8%，C 2 选择性为 46%，产物中 C2H4
8、/C2H6 摩尔比为 2.6。稳定性测试实验显示 BSCFCl0.04 的催化活性没有发生衰减，这表明该材料具备较好的催化活性稳定性。接着，我们又做了几组对比实验以考察氯掺杂及用笑气代替氧气作为氧源对 BSCF 催化性能的影响。结果表明不论用氧气还是笑气作为氧源，氯掺杂均提高了甲烷转化率及 C2 的选择性。但值得注意的是，当用笑气代替氧气作为氧源时，氯掺杂对 BSCF 催化性能的改进更明显。通过固定床上的催化活性测试证实氯掺杂改善了 BSCF 的甲烷氧化偶联性能后，我们进一步研究了氯掺杂 BSCF 透氧膜反应器的甲烷氧化偶联性能。实验结果再次表明，氯掺杂同时改善了甲烷的转化率及 C2 选择性，
9、但 C2 的收率改进不如固定床上采用笑气做氧源时改进明显。但是一个有趣的现象是，氯掺杂后最大 C2 收率所对应的温度由 850 oC 下降到了 800 oC，原因可能是氯掺杂增强了催化剂表面氧物种的活性，提高了甲烷在较低温度下的活化速率。最后，我们初步探索了氯掺杂对 BSCF 膜反应器乙烷氧化脱氢性能的影响。结果表明，氯掺杂显著地改善了 BSCF 的乙烷氧化脱氢性能。最大的乙烯选择性达到了 90%，要比 BSCF 上获得的最大收率高出约 12%。此外，BSCFCl 0.04上获得乙烷转化率也要远远高于 BSCF，这可能一方面与氯掺杂改善了催化剂表面氧物种活性有关，另一方面是由于氯掺杂改善 BS
10、CF 在低温下的透氧量。775 oC 时，BSCFCl 0.04 获得最大的乙烯收率约为 53%，而同样条件下 BSCF 上获得的最大的乙烯只有约 41%。关键词：透氧膜；钙钛矿；氯掺杂；甲烷氧化偶联；乙烷氧化脱氢IIIAbstractPerovskite-type oxides have been attracting considerable attention due to their wide applications in catalysis, superconductors, gas sensors, solid oxide fuel cell, ferroelectrics an
11、d ferromagnets. In addition to the above applications, membrane reactors based on perovskite-type oxides also show a large potential for process intensification of selective oxidation reactions of hydrocarbons because they can integrate oxygen separation and reactions into single operation unit to s
12、implify operation processes and cut down operating cost. However, these perovskite oxides are generally unstable due to the reducibility of hydrocarbons and possess low catalytic activity for the selective oxidation reactions or low oxygen permeation ability under the temperature of selective oxidat
13、ion reactions. Doping on cations sites (i.e. A or B site of ABO3 perovskite structure), in the past two decades, was the main strategy to explore new perovskite membrane materials with high structure stability, catalytic activity and oxygen permeation ability. However, so far, there are no reports a
14、bout the doping of perovskite oxides on anion site for the oxygen permeable perovsktie membrane. Actually, doping on anion site by halide is an effective way to improve the catalytic performance of hydrocarbons selective oxidation reactions for perovskite catalysts because the presence of halide ion
15、s in the perovskite lattices promotes the mobility of lattice oxygen. In this paper, we investigated the structure stability, catalytic activity and oxygen permeation ability of a novel chlorine doped perovskite oxide.The perovskite powders with nominal formulas Ba0.5Sr0.5Co0.8Fe0.2O3- (BSCF) and Ba
16、0.5Sr0.5Co0.8Fe0.2O3-Cl0.04 (BSCFCl0.04) were prepared by combined citrate acid and EDTA complexing method. X-ray diffraction analysis (XRD) indicated that both BSCF and BSCFCl0.04 powders formed complete cubic perovskite structure. X-Ray photoelectron spectroscope (Xps) revealed that chlorine dopin
17、g reduced the metal-oxygen bond energy and therefore enhanced the oxygen ion mobility. Oxygen temperature programmed desorption (O2-TPD) demonstrated that chlorine doping increased the oxygen reversible desorption capacity at 600900 oC.IVFirstly, we investigated the influence of chlorine doping on t
18、he oxygen ion conductivity of BSCF. At the temperature range from 575700 oC, BSCFCl0.04 showed much higher oxygen permeation flux than BSCF. For example, an oxygen permeation flux of 0.29 mLmin-1cm-2 could be obtained through a 1 mm thick BSCFCl0.04 membrane at 600 C which was about three times high
19、er than that through the undoped BSCF at the same operation condition. This verified the conclusion of XPS that chlorine doping increased oxygen ion mobility in the bulk of BSCF. Besides, no remarkable decline of oxygen permeation flux was observed in more than 120s hours long term oxygen permeation
20、 test at 600 oC, indicating that BSCFCl0.04 had undergone no significant phase degradation. The XRD patterns of the membrane before and after oxygen permeation test also confirmed it. Halogen doping is reported as an effective way to improve metallic oxides catalytic activity for selective oxidation
21、 reactions such as oxidative coupling of methane (OCM) and oxidative dehydrogenation of ethane (ODE). Therefore we also studied the OCM catalytic activity of chlorine doped BSCF on a fixed bed reactor. Furthermore, N2O was chosen as the oxygen source because it is a relatively weak oxidant, which is
22、 suitable for selective oxidation. A maximal per pass C2 (ethane and ethylene) yield of 30.7% was obtained at a CH4/N2O ratio of around 0.4 with a CH4 conversion of 66.8% and a C2 selectivity of 46.0 % at 850 oC. The molar ratio C2H4/C2H6 in the educt was about 2.6. In the process of long term OCM o
23、peration on BSCFCl0.04, we didnt find any decay of catalytic activity, which indicated BSCFCl0.04 was relative stable during the whole operation process. In addition, we conducted contrast experiments between BSCF and BSCFCl0.04 catalysts when used O2 or N2O as oxidant. The result showed that chlori
24、ne doping had indeed improved both CH4 conversion and C2 selectivity whether using O2 or N2O as oxidant. However, using N2O as oxidant made the improvement of chlorine doping more remarkable. Perovskite-type oxygen permeable membrane is considered as a promosing technology for process intensification of selective oxidation reactions of hydrocarbons by integrating oxygen separation and reactions into single operation unit to simplify operation processes and cut down operating cost. However, these oxides catalytic
