摘要
锰氧化物多相水氧化催化剂的研究
音频故事下载论文作者：耿智彬
指导教师：冯守华教授
专业名称：无机化学
摘要
利用太阳光能合成清洁燃料是解决能源问题的理想途径，因此，光催化裂解水制氢已成为新能源研究的热点。水氧化反应是将水分子氧化为氧气并放出质子的反应，在光催化裂解水过程中起到重要作用。作为一个四电子过程，水氧化反应的难度较大，已成为制约光催化裂解水效率提高的重要因素。因此，开发一种廉价、高效、稳定的水氧化催化剂是至关重要的。其中，多相水氧化催化剂具有稳定性好、易于大规模制备等优点，受到了人们的广泛关注。
在众多的多相水氧化催化剂中，锰氧化物催化剂是最有潜力一种。锰是廉价、环保、高丰度的元素，锰氧化物比贵金属氧化物和钴氧化物更适合大量应用。但是，水氧化催化对锰氧化物结构和组成的要求很
高，目前的锰氧化物催化剂都与理想结构相差甚远，导致水氧化活性较低。因此，要提高催化剂的水氧化活性，必须对锰氧化物的组成、结构和电子态进行精确调控，使催化剂更加适合水氧化催化。在本论文中，我们从结构和电子态的调控入手，合成了多种高效的锰氧化物多相水氧化催化剂：
1、在温和还原条件下合成了δ-MnO2–Mn3O4纳米复合材料。这种材料由δ-MnO2纳米片和Mn3O4纳米粒子紧密结合形成，由于构成δ-MnO2和Mn3O4的MnO6八面体结构参数和锰价态不同，两相的界面处形成了无序易变的结构、较弱的Mn-O键和Mn3+/Mn4+混合价态，这对水氧化催化十分有利。因此，δ-MnO2–Mn3O4纳米复合材料的水氧化活性远高于单组分的δ-MnO2纳米片和Mn3O4纳米粒子。通过还原剂剂量的调控，可以得到不同组成的催化剂，其中含有38% Mn3O4和62% δ-MnO2（锰摩尔比）的材料具有最好的水氧化活性TOF = 0.93 s-1。我们
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对δ-MnO2–Mn3O4纳米复合材料的结构、电子态和水氧化活性进行了详细的表征，探究了催化剂生长机理和构效关系，并详细分析了退火处理对催化剂结构和性能的影响。
2、我们用超声辅助还原法对Ca-水钠锰矿的结构和电子态进行调控，得到了更适合水氧化催化的改性
Ca-水钠锰矿催化剂。在改性过程中，超声和还原处理协同作用，在保留MnO2薄层结构的情况下，将Ca-水钠锰矿中大部分Mn4+还原为高活性的Mn3+，并剥开层状结构把活性辅助离子Ca2+暴露出来，形成类似自然界水氧化活性中心Mn4CaO5的结构。根据XRD谱图可知，改性Ca-水钠锰矿催化剂层状结构完全消失，而MnO2薄层结构保持不变。TEM表征显示改性Ca-水钠锰矿为单层MnO2薄片的无序堆叠结构，具有较高的比表面积。XPS谱图显示催化剂的锰平均价态接近+3价。改性Ca-水钠锰矿催化剂的水氧化活性可达TOF = 3.43 s-1，远高于典型的Ca-水钠锰矿。此外，我们也研究了改性催化剂的合成机理、最佳合成条件、最佳水氧化测试条件和退火对材料的影响。
3、我们对钙钛矿锰氧化物中A位的镧钙比例进行调控，合成了一系列具有不同结构和电子态的La1-x Ca x MnO3催化剂。La1-x Ca x MnO3催化剂为近似球形的纳米粒子，XRD谱图显示其为纯相的钙钛矿结构，晶格结构随着镧钙元素比例变化而变化。La1-x Ca x MnO3催化剂中影响水氧化活性的因素很多，包括Mn3+含量、晶格有序度、表面Ca2+数量、导电性等，因此催化剂的水氧化活性是由众多因素综合作用的结果。水氧化活性最佳的催化剂是锰平均价态为+3.7价的La0.25Ca0.75MnO3，较多的表面Ca2+和较大的晶格无序度是其高活性的主要因素。我们对钙钛矿钙锰氧化物元素组成与结构、电子态和性能的关系进行了探究。
回收站英文本论文中通过温和还原、超声处理、控制投料比等方法，对锰氧化物的组成、结构和电子态进行调控，得到了多种锰氧化物多相水氧化催化剂。这些催化剂的组成和结构更接近自然界水氧化中心Mn4
少儿剑桥英语CaO5，具有较高的水氧化活性或稳定性。与以往的研究相比，我们更加关注化学键和原子尺度的调控，以直接获得有利于水氧化催化的活性结构，这为进一步提高锰氧化物催化剂的水氧化性能提供了新的视角。
情人节翻译关键词：水氧化；锰氧化物；结构；电子态
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Abstract舞文弄墨的意思
The study of mangane oxide catalysts for heterogeneous water oxidation
Author: Zhibin Geng
Supervisor: Prof. Shouhua Feng
Major: Inorganic Chemistry
Abstract
civilianIt is an ideal way to solve the energy problem by photocatalytically splitting water into hydrogen, whic
h utlizizes solar energy to produce clean fuel. Water oxidation reaction plays an important role in the process of photocatalytic water splitting, which oxidates water molecules into oxygen and releas protons. As a four electron process, the water oxidation reaction is much more difficult than hydrogen evlution reaction, which has become an important factor restricting the improvement of overall photocatalytic water splitting activity. Therefore, it is significant to develop a cheap, efficient and stable water oxidation catalyst.
Mangane is a cheap, environmentally friendly, and earth abundant element. Mangane oxide is one of the most promising catalysts for water oxidation which is more suitable for mass application than noble metal oxide and cobalt oxide. In green plant, the water oxidation complex (OEC) in photosynthesis is just compod of mangane oxide clusters, which provides an excellent example for artificial mangane oxide water oxidation catalyst. In the longterm study of mangane oxide catalyst and the OEC, people summarized the structure-activity relationship of mangane oxide water oxidation catalyst. Mn3+is generally considered the active mangane ion in water oxidation; flexible structure and long Mn-O bond is conducive to water oxidation catalysis; Ca2+ doping can significantly improve water
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couples retreatoxidation activity of mangane oxide. However, the existed mangane oxides can only partly meet the conditions, resulting in lower water oxidation activity. Therefore, it is necessary to regulate the structure and electronic state of mangane oxide in order to improve the water oxidation activity of the catalyst.
brown怎么读In this thesis, we fabricate veral kinds of mangane oxide catalyst for the water oxidation catalysis bad on regulation of structure and electronic state: 1, δ-MnO2–Mn3O4nanocomposites were synthesized via a mild reduction condition. This material is compod of δ-MnO2 nanosheets and Mn3O4 nanoparticles. Owing to the different structure parameters of MnO6octahedral in δ-MnO2and Mn3O4, the interface between two phas formed disordered structure, weak Mn-O bond, and Mn mixed valence of Mn3+/Mn4+. This configuration is favorable for water oxidation catalysis. Benefit from the active interface, the water oxidation activity of δ-MnO2–Mn3O4nanocomposites is much higher than that of the single component δ-MnO2nanosheets or Mn3O4nanoparticles. By controlling the reduction do, δ-MnO2–Mn3O4nanocomposites of different compositions can be obtained, the catalyst containing 38% Mn3O4and 62% δ-MnO2hold the best water oxidation activity of TOF = 0.93 s-1. We chatacterized the structure, electronic states and water oxidation activity of δ-
MnO2–Mn3O4nanocomposites, explored the growth mechanism and the structure-activity relationship of the catalyst, and analyzed the effect of annealing treatment on the structure and properties of catalyst.
2, We utilize an ultrasonic assisted reduction process to optimi the structure and electronic state of typical Ca-birnessite, obtaining a modified Ca-birnessite catalyst which is more suitable for water oxidation catalysis. In the modification treatment, the ultrasonic treatment synergizes with the reduction process, reducing most Mn4+in Ca-birnessite into active Mn3+, delaminating the layer structure to expo active assisted ion Ca2+, and forming a similar structure to the natural water oxidation center Mn4CaO5. According to the XRD spectra, the layered structure of the modified Ca-birnessite catalyst completely disappeares, while the structure of MnO2 thin film remains unchanged. The TEM characterization showed that the modified IV
Abstract
Ca-birnessite is a disordered stacking structure of monolayer MnO2with a high specific surface area. The XPS spectra showed that the average valence of mangane is clo to +3. The water oxidation activity of the modified Ca-birnessite catalyst is up to TOF = 3.43 s-1, which is much higher than typi
cal Ca-birnessite. In addition, we studied the synthesis mechanism, the best synthesis condition, the best water oxidation condition and the effect of annealing treatment on the material.
3, Perovskite type calcium mangane oxide water oxidation catalysts are prepared by sol-gel method. The perovskite structure has excellent stability, when the composition, structure and electronic states of perovskite type mangane oxides meet with the requirements of water oxidation catalysis, an excellent water oxidation catalyst with both high activity and high stability will be formed. A ries of La1-x Ca x MnO3catalysts with different structures and electronic states have been synthesized by adjusting the ratio of La/Ca of A site in perovskite mangane oxide. The morphology of La1-x Ca x MnO3 catalyst is nearly spherical. The XRD spectra show that it is a pure perovskite structure, and the lattice structure changes with the ratio changes of lanthanum and calcium. Many factors influence the water oxidation activity of La1-x Ca x MnO3 catalysts, including Mn3+ content, lattice ordered degree and surface Ca2+ number, conductivity, etc. Thus, water oxidation activity of the catalyst is determined by the comprehensive effect of a number of factors. The best catalyst for the oxidation water is La0.25Ca0.75MnO3 with an average mangane valence of +3.6, large numbers of surface Ca2+ions and the larger lattice disordered are the main factors of high activity. We studied the relationship between the composition, structure, electronic state and the properties of perovskitealcium mangane oxides.
In this thesis, the composition, structure and electronic state of mangane oxides were regulated by the methods of moderate reduction, ultrasonic treatment and control of feed ratio. Several kinds of fine mangane oxide water oxidation catalysts are fabricated. The composition and structure of the catalysts are clor to the natural water oxidation center of Mn4CaO5, and show high water oxidation activities and stability. Compared with the previous rearch, we pay more attention to the
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