Study on Ru-based Ammonia Synthesis Catalysts Supported on Complex Oxides Derived from Hydrotalcite-type Compounds

摘要本文采用并流共沉淀法合成一系列水滑石类化合物，用于制备负载型氨合成钌催化剂的复合氧化物载体。其中，由镁铝水滑石制备的镁铝复合氧化物载体性能最好，以之为载体、KNO3为助剂的钌催化剂在0.2MPa下的氨合成活性高达40mLNH3·h-1·g-1，且具有良好的耐热性能，经500℃以上高温热处理25h，共计使用约120h后仍保持较高的催化活性。镁铝复合氧化物载体的性能与制备条件的选择密切相关。相对铵碱液而言，钠碱液为沉淀剂能够制备出更优良的载体，其载体微观形貌为杂乱的六边形片层堆积结构，对钌晶粒的烧结有一定的抑制作用，使催化剂具有高而稳定的活性。钠碱液沉淀剂的用量和滴料终点的pH值对复合氧化物的...Abstract Novel complex oxides were prepared as the supports of ruthenium-based catalysts for ammonia synthesis by calcinating a series of hydrotalcite-type compounds that were obtained from co-precipitation. Of all the synthesized supports, magnesium-aluminum complex oxide Mg(Al)O showed extraordinary performance. The catalyst Ru/Mg(Al)O promoted with KNO3 exhibited significantly high ...学位：工程硕士院系专业：化学化工学院化学工程系_工业催化学号：20023301

Effects of Fluoride on Activities of Ru-based Ammonia Synthesis Catalysts

[中文文摘]以MgO为载体 ,分别用KF ,KNO3 ,BaF2 和BaO为促进剂前驱体制备钌基氨合成催化剂 ,并用X射线衍射 (XRD)、高分辨透射电子显微镜 (HRTEM)和催化剂性能评价等方法考察了不同促进剂前驱体对钌基氨合成催化剂的影响 .结果表明 ,电负性比氯大的氟的引入能提高催化剂的活性 ,在KF Ru/MgO催化剂中 ,F与载体的O发生交换 ,改变了载体的结构和表面性质 ,从而导致金属载体相互作用情况的不同以及金属分散度的提高 ,因而有利于催化活性的提高 .同时 ,当F以BaF2的形态存在时也能提高催化活性。[英文文摘]A series of Ru based ammonia synthesis catalysts supported by magnesia with different promoter precursors were prepared. The effects of different promoter precursors on the catalysts were investigated by XRD, HRTEM and performance evaluation techniques. The results indicated that the activities of catalysts were increased by the introduction of fluoride and some oxygen of magnesia was exchanged with fluoride in KF-Ru/MgO catalyst. It was suggested that the exchange of oxygen and fluoride changed the structure and surface property of support , hence improving the metal dispersion and the different interactions of ruthenium and the support . Consequently , the activity of catalyst prepared with KF was higher. At the same time , the activity of catalyst prepared by BaF2 was also higher than the one prepared by BaO, though the configuration of fluoride and barium was BaF2.国家自然科学基金(Nos.20273053,20023001,299330 40); 国家重点基础研究发展规划(No.001CB108906)资助项目

High-index-faceted platinum nanoparticles: insights into structural and thermal stabilities and shape evolution from atomistic simulations

National Natural Science Foundation of China [51271156, 11204252]; Natural Science Foundation of Fujian Province of China [2013J06002]; Specialized Research Fund for the Doctoral Program of Higher Education of China [20130121110012]High-index-faceted Pt nanoparticles exhibit exceptional electrocatalytic activity owing to the high density of low coordinated sites on their surface, and thus have attracted extensive studies over the past few years. In this study, we have employed atomistic simulations to systematically investigate the structural and thermal stabilities and shape evolution of Pt nanoparticles with different high-index facets, that is, tetrahexahedra enclosed by {hk0} facets, trapezohedra by {hkk} ones, and trisoctahedra by {hhk} ones. The results show that {221} faceted trisoctahedral nanoparticles display the best structural and thermal stabilities while {410} faceted tetrahexahedral ones display the worst. The shape stability of these nanoparticles generally decreases in the order from trapezohedron to tetrahexahedron to trisoctahedron. For the same type of polyhedron, the structural, thermal and shape stabilities of the nanoparticles all decrease according to the order of {2kl}, {3kl} and {4kl} facets. Further analyses have discovered that a large proportion of high-coordinated surface atoms are beneficial for enhancing both the thermal and shape stabilities. This work provides an in-depth understanding of surface structures and thermodynamic evolution of high-index-faceted metallic nanoparticles

Tetrahexahedral Pt-Pd alloy nanocatalysts with high-index facets: An atomistic perspective on thermodynamic and shape stabilities

Metallic nanoparticles with high-index facets exhibit exceptional electrocatalytic activity owing to the high density of low coordination sites at the surface, thus they have attracted intense interest over the past few years. Alloying could further improve their catalytic activity by the synergy effects of high-index facets and electronic structures of components. Using atomistic simulations, we have investigated thermodynamic and shape stabilities of tetrahexahedral Pt-Pd alloy nanoparticles respectively bound by {210} and {310} facets. Energy minimization through Monte Carlo simulations has indicated that the outermost layer is predominated by Pd atoms while Pt atoms preferentially occupy the sub-outermost layer of nanoparticles. Molecular dynamics simulations of the heating process have shown that the {210} faceted nanoparticles possess better thermodynamic and shape stabilities than the {310} faceted ones. The coordination numbers of surface atoms were used to explore the potential origin of the different stabilities. Furthermore, a high Pt ratio will help enhance their stabilities. For both faceted nanoparticles, the melting has homogeneously developed from the surface into the core, and the tetrahexahedra have finally evolved into sphere-like shape prior to the overall melting. These results are helpful for understanding the composition and thermodynamic properties of high-index faceted nanoparticles, and are also of practical importance to the development of alloy nanocatalysts. ? 2014 The Royal Society of Chemistry

Single-crystalline and multiple-twinned gold nanoparticles: an atomistic perspective on structural and thermal stabilities

National Natural Science Foundation of China [51271156, 11204252]; Natural Science Foundation of Fujian Province of China [2013J06002]; Fundamental Research Funds for the Central Universities of China [2012121010]Morphologies of gold nanoparticles play an important role in determining their chemical and physical (catalytic, electronic, optical, etc.) properties. Therefore, a fundamental understanding of the morphological stability is of crucial importance to their applications. In this article, we employed atomistic simulations to systematically investigate the structural and thermal stabilities of gold particles with eight representative nanoshapes, including single-crystalline and multiple-twinned structures. Our investigation has revealed that the truncated octahedron and the octahedron possessed the best structural stability, while the tetrahedron and the icosahedron did the worst. Further analyses have discovered different thermal stabilities and diverse melting behaviors in these particles. Especially, an inhomogeneous melting of the icosahedron was disclosed, and the relevant mechanism was elucidated. This study provides significant insight not only into the experimental preparation of gold nanoparticles but also into the design of gold nanostructures with both high catalytic activity and excellent stability

红树林区污水对藻类种群结构的影响

为了解红树林生态系统的功能，在深圳福田红树林沼泽进行生活污水排放对藻类种群结构及污染生态影响的研究。在海水退潮时，将生活污水排入红树林区，调查藻类的种类组成和数量变化。当污水排入红树林后，大部分藻类不能适应生境的剧变而死亡，只有少数适​​应性强的种类可以存活。以扁圆囊裸藻(Trachelomomascurta)、裸藻(Euglenaspp)、线性棒条藻(Rhabdodermalineara)、鱼腥藻(Anabaenaconstricta)为典型污染指示种类。放污水前后，底栖藻类生物量总量(叶绿素T)不呈现显著差异。近海水域藻类基本为自生地藻类，以硅藻(Bacillariophyta)为优势类群。藻类主要根据季节更替而出现种类季节演替及生物量的季节波动。污水排放对近海藻类生长有一定的促进作用，红树林具有净化、吸收污染物的功能，但必须严格控制污水排放量

InGaAsP/InP DC-PBH型单管激光器可靠性

本文介绍InGaAsP/InPDC—PBH型LD单管寿命试验、初期筛选老化及高低温循环实验情况。其结果是50℃时MTTF大于4000小时,采用0.9eV激活能外推室温（20℃）下,中值寿命大于10万小时,所观察到的寿命模式符合对数正态分布

初中生亲子关系与逆反:孝道的中介作用

探讨初中生亲子关系与逆反的关系及孝道的中介作用。选取北京市三所中学275名初二学生(男生134名,女生141名),采用《青春期逆反心理问卷》《中学生孝道问卷》《初中生亲子关系特性量表》进行调查。结果发现亲子关系的理解交流维度负向预测初中生逆反心理;孝道在这一关系中起完全中介作用。研究表明初中生亲子关系越好则逆反越少,理解交流的亲子关系有利于使初中生形成孝道态度,从而减少逆反心理。</p