铈基氧化物催化氧化柴油车排气碳烟性能研究

发布时间：2019-05-31 18:42

【摘要】：柴油发动机由于燃油效率高、功率大以及较低的CO和挥发性烃类有机化合物(VOC)排放等优点,在重型载重车与长途运输车中得以广泛使用。然而柴油发动机排气废气中碳烟颗粒物含量较高,且绝大多数粒径小于0.3μm,能够对人体健康以及生态环境造成很大危害。要有效去除排气碳烟,可以通过结合耐高温过滤器和碳烟低温燃烧催化剂的技术实现,低温条件下催化剂催化碳烟燃烧的活性和稳定性至关重要。在铈基氧化物中,铈锆复合氧化物催化体系由于具有优异的物理化学性能具有潜在催化碳烟燃烧研究价值。本文以铈锆复合氧化物为研究对象,通过不同的合成方法、掺杂改性等对催化体系催化碳烟燃烧性能进行研究。利用X-射线粉末衍射(XRD)、比表面积(BET)、扫描电镜(SEM)、光电子能谱(XPS)、傅里叶红外(FT-IR)以及H_2-程序升温还原(TPR)和程序升温氧化(TPO)等技术对材料进行表征和催化活性评价,并系统考察催化剂活性的影响因素,得出较为理想的研究结果。主要结论如下:1.采用溶胶凝胶法、水热法、共沉淀法和热分解法等制备出Ce_(0.8)Zr_(0.2)O_2复合氧化物。研究结果表明,5种方法所合成的Ce_(0.8)Zr_(0.2)O_2均能形成立方萤石结构的铈锆固溶体;在松散接触条件下,催化剂的比表面积(SBET)大小更能体现出其催化碳烟燃烧的活性,水热法合成的Ce_(0.8)Zr_(0.2)O_2因具有最大的SBET而显示出最高的催化碳烟燃烧能力;在紧密接触条件下,催化剂的还原性能和储氧能力对其催化碳烟燃烧活性产生重要影响,溶胶凝胶法所制得的Ce_(0.8)Zr_(0.2)O_2样品因具有最大的储氧量而表现出最高的催化碳烟燃烧活性。2.采用溶胶凝胶法制备Ce_(0.65-x)Co_xK_(0.15)Zr_(0.2)O_2系列催化剂。研究结果表明,Co离子难以大量扩散至CeO_2晶格中,而是以Co3O4粒子形式分散在样品表面。老化前催化剂表面Co3O4颗粒的数量和尺寸对催化剂的催化活性起关键性作用,而进入到CeO_2晶格中的钴离子则对提高催化剂的抗老化能力产生重要影响。当x=0.23时,催化剂表面出现大量具有高活性的细小Co3O4粒子,催化碳烟燃烧活性最高,Ti与Tm分别为321℃与355℃;当x=0.15时,催化剂老化前并未表现出优异的催化活性,但经老化后,因具有较多钴铈锆固溶体而显示出了最高的稳定性与催化碳烟燃烧活性,其Ti与Tm仍可达375℃与439℃。3.采用溶胶凝胶浸渍法在SiC上对钾、钴改性的铈锆复合催化剂进行负载。结果表明,负载后各样品催化碳烟燃烧能力都出现不同程度降低。其中,碳烟在样品K-Co-Ce-Zr/SiC上具有最低的燃烧温度与最快的氧化速率,Tm与平均燃烧速率分别为428℃和17.01μg/s,且经过5次循环使用后仍具较优的催化碳烟燃烧能力,显示出较好的稳定性。在该系列催化剂中,Co修饰铈锆复合氧化物后,通过提高表面氧的活性而提高催化剂的催化活性;当催化剂中存在K物种时,主要通过改善碳烟与催化剂的接触状况而有效促进了碳烟的燃烧。
[Abstract]:The diesel engine has the advantages of high fuel efficiency, large power and low CO and volatile hydrocarbon organic compounds (VOC) emission, and is widely used in heavy-duty truck and long-distance transport vehicle. however, that content of the carbon smoke in the exhaust gas of the diesel engine is high, and the vast majority of the particle size is less than 0.3. m In ord to effectively remove that exhaust soot, the activity and the stability of the catalyst-catalyzed soot combustion at low temperature can be very important by the technology of combining the high-temperature-resistant filter and the low-temperature combustion catalyst of the soot. In the base oxide, the composite oxide catalyst system has the potential for catalytic carbon smoke combustion due to its excellent physical and chemical properties. In this paper, the catalytic carbon-smoke combustion performance of the catalytic system was studied by means of different synthesis methods, doping modification and so on. The materials were characterized by X-ray powder diffraction (XRD), specific surface area (BET), scanning electron microscope (SEM), photoelectron spectroscopy (XPS), Fourier infrared (FT-IR) and H _ 2-program temperature-increasing reduction (TPR) and program temperature-increasing oxidation (TPO). The influence factors of the activity of the catalyst are investigated and the ideal results are obtained. The main conclusions are as follows:1. Ce _ (0.8) Zr _ (0.2) O _ 2 composite oxide was prepared by sol-gel method, hydrothermal method, co-precipitation method and thermal decomposition method. The results show that the Ce _ (0.8) Zr _ (0.2) O _ 2 synthesized by the five methods can form a cubic solid solution of the cubic fluorite structure. Under the condition of loose contact, the specific surface area (SBET) of the catalyst can reflect the activity of the catalytic soot combustion. Ce _ (0.8) Zr _ (0.2) O _ 2 synthesized by hydrothermal method shows the highest catalytic carbon-smoke combustion ability due to the maximum SBET; under the condition of close contact, the reducing energy and oxygen storage capacity of the catalyst have an important influence on the catalytic carbon-smoke combustion activity, The Ce _ (0.8) Zr _ (0.2) O _ 2 sample prepared by the sol-gel method has the highest catalytic carbon-smoke combustion activity due to the maximum oxygen storage capacity. Ce _ (0.65-x) Co _ xK _ (0.15) Zr _ (0.2) O _ 2 series catalyst was prepared by sol-gel method. The results show that the Co ion is difficult to diffuse into the CeO _ 2 crystal lattice, but it is dispersed in the sample surface in the form of Co3O4 particles. The number and size of the Co3O4 particles on the surface of the pre-aging catalyst plays a key role in the catalytic activity of the catalyst, and the cobalt ions entering the CeO _ 2 crystal lattice have an important influence on the anti-aging ability of the catalyst. When x = 0.23, a large amount of fine Co3O4 particles with high activity appeared on the surface of the catalyst, the combustion activity of the catalytic carbon smoke is the highest, and the Ti and the Tm are 323.degree. C. and 355.degree. C., respectively; when x = 0.15, the catalyst does not exhibit excellent catalytic activity before aging, but after aging, The highest stability and the catalytic carbon-smoke combustion activity are shown due to the cobalt-rich solid solution, and the Ti and Tm can still reach the temperature of 375 DEG C and the temperature of 439 DEG C. A sol-gel impregnation method was used to load the composite catalyst of potassium and cobalt modified by the method of sol-gel impregnation. The results showed that the catalytic carbon-smoke combustion ability of each sample decreased in different degrees after loading. The carbon smoke has the lowest combustion temperature and the fastest oxidation rate on the sample K-Co-Ce-Zr/ SiC, the Tm and the average combustion rate are 428 DEG C and 17.01. m In the series of catalysts, the catalytic activity of the catalyst is improved by improving the activity of the surface oxygen after the Co-modified polyoxyalkylene compound oxide, and the combustion of the soot is effectively promoted by improving the contact condition of the soot and the catalyst when the K species are present in the catalyst.
【学位授予单位】：贵州师范大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：U469.74

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