【作者】 田雨；

【导师】 吕志；

【作者基本信息】 北京化工大学 ， 化学， 2012， 硕士

【摘要】 层状复合金属氢氧化物（LDHs）也被称为阴离子黏土，是一种新型无机功能材料。LDHs具有独特的结构和功能特性，在众多领域得到了广泛的应用，如催化、吸附、医药等。然而LDHs没有内比表面，比表面积都比较小，这在很大程度上限制了它的应用。因此，增加LDHs材料的比表面积是一个很重要且值得研究探索的课题。LDHs的比表面积主要基于它的外表面积，为了提高比表面积，减小LDHs粒子的厚度就成为首要解决的问题。通过传统方法，如共沉淀法、水热法等制备的LDHs比表面积都较小，大约为20⁸0m²/g，晶粒厚度一般为20⁵0nm。本论文提出了一种简便易行的新方法，通过添加助剂来抑制水滑石c方向上的生长（垂直于层板的堆积方向），制备出了粒子厚度<15nm、比表面积>160m²/g的MgAl-CO3-LDHs。研究结果表明：1.研究了三种助剂（十二烷基苯磺酸钠、聚乙二醇、十二烷基硫酸钠）和制备方法对MgAl-CO3-LDHs比表面积的影响。结果表明，采用双滴法，以聚乙二醇（PEG）为助剂时的效果最好，制备出的LDHs样品颗粒厚度最薄（14.2nm）、比表面积最大（142.6m²/g）。而以十二烷基硫酸钠（SDS）为助剂不能制备出大比表面积的LDHs；以十二烷基苯磺酸钠（SDBS）为助剂的效果不如聚乙二醇好。PEG通过氢键作用力吸附在LDHs表面形成吸附层，抑制其厚度方向（c方向）的生长，吸附层之间存在空间位阻效应，能阻止LDH晶胚之间的团聚和聚合，从而制备出晶粒厚度很薄的LDHs。2.系统研究了聚乙二醇不同添加时间、混合时间、聚合度、浓度、添加顺序及晶化温度、碱量对LDHs粒子厚度、比表面积的影响。结果表明，采用共沉淀法通过同步滴加盐、碱及助剂三种溶液，滴加完毕后升温到95℃，且助剂PEG-1000浓度为8g/L时制备出的LDHs样品粒子厚度为10.8nm，比表面积为160.5m²/g。PEG聚合度增大，其在水中的分子链增长，更容易交联在一起，使产物粒子厚度变大。PEG通过氢键吸附在LDHs表面存在有饱和吸附值，超过饱和吸附时游离在溶液中的PEG起到连接粒子的作用，使LDHs晶粒团聚长大。先在溶液中加入PEG然后再滴加盐、碱溶液，在溶液体系中存在大量的PEG超过了其饱和吸附值，起到的主要是连接粒子的作用；待盐、碱溶液滴加完毕后再加入PEG，LDHs已经开始生长，PEG起到的作用就很小了。NaOH和Na₂CO₃作为沉淀剂对LDHs的生长具有重要的作用，调节其与金属离子合适的比例来达到实验目的。3.研究了晶化时间、固含量和镁铝比对LDHs粒子厚度及比表面积的影响。结果表明，在晶化时间6-8小时，固含量<9wt%，镁铝比从2.5到4时，均能制备出大比表面积的MgAl-CO₃-LDHs；并在晶化时间6h，固含量1.38%，镁铝比为3时，制备出了比表面积为167.7m²/g的LDHs样品。4.通过硫转移性能测试装置来评价样品的氧化吸硫性能，此装置为改装的热重天平，具有多组气体调节和混合系统，可在多种气氛之间切换，并模拟FCC再生器环境和提升管反应器环境，对制备出的大比表面积MgAl-CO3-LDHs样品进行了氧化吸硫性能评价。更多还原

【Abstract】 Layered double hydroxides （LDHs） often called as anionic clays, area kind of novel inorganic functional materials. LDHs have uniquestructure and functional characteristics and find application in diverseareas such as catalysts, as adsorption, medicine, etc. However, the LDHshave a small specific surface area, because they have no specific internalsurface, which restricted their promoted application. Therefore, it is avery important and worth exploring topic to increase the specific surfacearea of LDH materials.To increase the specific surface area of LDH materials, reducing thethickness of particles become the essential problem for that the specificsurface area of LDHs is determined by the surface area of LDHs. TheLDHs synthesized by traditional methods such as co-precipitation,hydrothermal process display small specific surface area （20-80m²/g） andlarge particle thickness （20-50nm）.In this article, the MgAl-CO3-LDHs with thin particle thickness （<15nm）, high specific surface area （>165.9m²/g） were synthesized by a simple new method by adding additive. The additive inhibits the crystalgrowth in c direction （the stacking direction, perpendicular to the layers）.The details are shown below:1. The influence of additives （sodium dodecyl benzene sulfonate,sodium dodecyl sulfate and polyethylene glycol） and preparationmethods on specific surface area of LDHs have been studied. Thecomparison of experiment showed that: Synthetize of LDHs usingdouble-drop method with PEG as additive, display thinnest thickness（14.2nm） and highest specific surface area （142.6m²/g）. The LDHssynthetized with sodium dodecyl benzene sulfonate or sodium dodecylsulfate, display the relatively small specific surface area. PEG absorptedon the surface of LDHs and formed absorption layer through thehydrogen bondind force. The stereo-hindrance effect between absorptionlayers inhibited the reunion and polymerization of LDH embryos,inhibited the growth in c direction, and resulted in the generation ofultrathin LDHs.2. The influence of adding time, mixing time, degree ofpolymerization, adding order, concentration of PEG, crystallizationtemperature, and the amount of alkali on particle thickness and specificsurface area of LDHs have been studied. The LDHs with the particlethickness10.8nm and specific surface area160.9m²/g have beensynthesized under the concentration of PEG-10008g/L, and added salt, alkaline, PEG-1000solutions simultaneously. With the increasing of PEGpolymerization degree, the molecular chain of PEG in solution increaseswhich facilitates the occurrence of cross-linking effect and results in theincrease of particle thickness. When the concentration of PEG exceedsthe saturated adsorption value in solution, the free PEG will connect theparticles together and make the LDHs grains grow up together. Addingthe PEG earlier than the salt and alkali solution, the high concentration ofPEG in solution will exceed the saturated adsorption value and connectthe particles. The function of PEG would be small if added the PEG afterthe introducing of the salt and alkali solutions for that the LDHs hadalready grew. The precipitants of NaOH and Na₂CO₃have an importantrole on the growth of LDHs. Experimental purposes can be obtained byadjusting the concentration proportion of of NaOH and Na₂CO₃to metalions.3. The influence of crystallization time, solid content and the ratioof Mg/Al on the particle and specific surface area of LDHs have beensystematic investigated. The results show that the MgAl-CO3-LDHswith high specific surface area can be synthesized under the conditions（crystallization time:6-8h, Mg/Al ratio:2.5-4, solid content:<9wt%）.The condition to synthesis the LDHs with the specific surface area of167.7m²/g is as follows: crystallization time is6h, solid content:1.38%,Mg/Al ratio is3. 4. The device for SO_xpick-up performance was designed on a basisof thermogravimetric instrument. It can provide different reactionatmosphere by multiple sets of gas regulation and hybrid systems, andswitch reaction atmosphere by multiplexing valve. The environment ofregenerator and riser reactor of FCC was simulated, and the SO_xpick-upperformance of MgAl-CO₃-LDHs with high specific surface area hasbeen evaluated successfully.更多还原