| 题名 | 锰氧化物催化剂上低温催化完全氧化乙醇的研究 |
| 作者 | 张洁 |
| 学位类别 | 博士 |
| 答辩日期 | 2014-05 |
| 授予单位 | 中国科学院研究生院 |
| 授予地点 | 北京 |
| 导师 | 贺泓 |
| 关键词 | OMS-2催化剂 MnO2 catalysts Ethanol oxidation Low temperature oxidation Alternative fuel vehicles ; MnO2氧化物催化剂 低温催化氧化 乙醇催化氧化 乙醇燃料 车尾气净化 OMS-2 catalysts |
| 其他题名 | Study of Manganese oxide catalysts on ethanol complete oxidation |
| 学位专业 | 环境科学 |
| 中文摘要 | 挥发性有机物（VOCs）是重要的一类大气污染物，并对生态环境和人体健康造成危害。机动车尾气排放是 VOCs产生的主要来源之一。乙醇作为一种常见的挥发性有机物，存在于以乙醇为混合燃料的机动车尾气中，乙醇混合汽油为动力的机动车尾气中释放的乙醇气体及其中间氧化产物乙醛，对人体健康具有直接危害。因此研究乙醇催化完全氧化技术，已成为改善人们生活环境质量的迫切任务。现有 Pt/Rh三效催化剂对机动车尾气中醇类去除效率较低，而锰氧化物是一种极具前景的催化氧化乙醇完全分解为无害的 H2O和CO2的高效催化剂。 本论文制备了八面体分子筛型锰氧化物（OMS-2）催化剂用于乙醇催化完全氧化反应，对催化剂进行了系统的表征，探讨了影响 OMS-2催化剂活性的因素。取得的创新性结果如下： 采用水热合成法制备了一系列催化剂，考察了以不同 Mn2+离子源（MnCl2, MnNO3, MnSO4, Mn(CH3COO)2）为前驱体制备的 OMS-2对乙醇气体完全氧化的能力。制备的所有OMS-2均为纳米棒结构，前驱体不会影响催化剂的形貌特征。以 MnSO4为前驱体制备而得的催化剂活性最优；以 Mn(CH3COO)2为前驱体制备的催化剂活性最差；以 MnSO4为前驱体的催化剂在 140℃可实现乙醇完全氧化为 CO2。在 OMS-SO4催化剂上检测到 SO42-残留，SO42-的残留削弱了 OMS-2催化剂 Mn-O键的强度并提高了晶格氧的浓度和活泼性，从而引起催化剂活性的改变； 采用离子交换法制备了不同 K+含量的 OMS-2锰氧化物八面体分子筛催化剂，考察了其对催化剂催化乙醇完全氧化反应活性和选择性的影响。结果表明，随着 K+浓度的升高，副产物乙醛的选择性逐渐降低，而催化乙醇完全氧化的活性逐渐提高。通过系列表征研究发现，增加 K+的含量会提高 OMS-2催化剂的晶格氧浓度，同时 K+含量的提高会减少催化剂表面的强酸位点，从而降低了对副产物乙醛的选择性，这是其提高 OMS-2催化剂催化完全氧化乙醇活性的重要原因； 采用水热合成法制了 α-MnO2，β-MnO2，γ-MnO2和 δ-MnO2催化剂。催化剂对乙醇氧化活性顺序为 α-MnO2 > δ-MnO2 > γ-MnO2 > β-MnO2。不同晶型的 MnO2催化剂比表面积差异显著，但是经过单位面积乙醇转化率归一化计算，发现比表面积并不是影响乙醇氧化活 性的重要原因。α-MnO2催化剂具有较高的晶格氧浓度，这是催化剂具有良好活性的重要原 因。 |
| 英文摘要 | Volatile organic compounds (VOCs) are major organic pollutants in the atmosphere and very harmful to human health. Industrial pollution and vehicle emissions are the main sources of VOCs. Ethanol is a widely used solvent and an important supplemental fuel for vehicles, and is recognized as a contributor to the photochemical formation of smog, so it is of great importance to investigate suitable methods for ethanol elimination. In addition, alcohol is quite resistant to decomposition by Pt/Rh based three-way catalysts. Therefore, more efficient catalysts for the reduction of ethanol emissions are needed. In this work, manganese oxides with the structure of a cryptomelane-type octahedral molecular sieve (OMS-2) were synthesized by a hydrothermal method and then tested for the catalytic oxidation of ethanol. All catalysts were characterized by a variety of techniques. The reaction mechanisms for ethanol oxidation on OMS-2 catalysts were discussed. The main results are summarized as follows: (1) The catalyst synthesized with MnSO4 as precursor (OMS-SO4) demonstrated great activity in ethanol oxidation. The complete conversion of ethanol to CO2 (800ppm, GHSV: 36000 h-1) was achieved at 120 °C over the OMS-SO4 catalyst. The prepared OMS-2 catalysts showed essentially the same diffraction pattern as synthetic cryptomelane and displayed fibrous morphologies. The results showed that precursor differences do not change the structure of the OMS-2 material. Trace amounts of the residual sulfation species (SO4/catalyst= 0.5 w/w %) were found to remain on OMS-2 catalysts and the sulfation species greatly modified the surface acidity of the OMS-2 material. Residual sulfation species weakened the Mn-O bond strength and changed the lattice oxygen concentration of the OMS-2 catalyst, which then effectively promoted the catalytic activity in ethanol oxidation. (2) OMS-2 nanorods with different K+ concentration were prepared by an ion-exchange method. The activities of the catalysts decreased with decreasing K+ concentration, while the yield of acetaldehyde increased greatly when the K+ concentration decreased. The effect of K+ concentration on the lattice oxygen activity of OMS-2 was studied by TGA and H2-TPR. The results show that increasing the K+ concentration leads to a considerable enhancement of the lattice oxygen activity in OMS-2. Facile accessibility and a high concentration of lattice oxygen benefited the oxidation process. When the K+ concentration decreased, the amount of strong acid sites increased, resulting in large acetaldehyde formation and poor activity for catalysts. (3) α-, β-, γ- and δ-MnO2 nanorods were synthesized by a hydrothermal method. The effect of crystal phase on the activities of the MnO2 nanorods was investigated. The activities of the catalysts decreased in the order α-MnO2 >δ-MnO2 > γ-MnO2 >β-MnO2. The BET surface areas of the α-, β-, γ- and δ-MnO2 nanorod catalysts exhibited the same tendency as their ethanol oxidation activity. The activity for ethanol oxidation was mainly influenced by the lattice oxygen concentration, and crystal phase also played an important role in ethanol oxidation on MnO2 catalysts. |
| 公开日期 | 2015-07-07 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.rcees.ac.cn/handle/311016/15708]  |
| 专题 | 生态环境研究中心_固体废弃物处理与资源化实验室 |
| 推荐引用方式 GB/T 7714 | 张洁. 锰氧化物催化剂上低温催化完全氧化乙醇的研究[D]. 北京. 中国科学院研究生院. 2014. |
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