Flexible,dicationic imidazolium salts for in situ application in palladium‐catalysed Mizoroki–Heck coupling of acrylates under aerobic conditions

The synthesis, characterization and in situ catalytic performance of new unsymmetric N,N′‐disubstituted imidazolium‐based dicationic salts in Mizoroki–Heck coupling of acrylates with aryl bromides under aerobic conditions are described. A series of flexible dicationic salts with varying steric and electronic properties were synthesized in good to excellent yields. All the salts were well characterized using spectroscopic techniques. X‐ray diffraction analysis of two salts with the same dicationic backbone and different counter anions shows that the ligand adopts two different conformations which are influenced by the nature of the anion. Thus, the ligand is capable of changing its conformation according to the change in environment due to its flexible nature. All the synthesized imidazolium salts were found to be active in in situ palladium‐catalysed Mizoroki–Heck coupling under aerobic conditions. Amongst the salts, the hydroxyl‐functionalized imidazolium salt, incorporating the features of both bidentate chelating O,O ligand and carbene, shows the maximum catalytic activity. A variety of aryl and heteroaryl methyl and ethyl cinnamates were synthesized using these imidazolium salts as preligands. In addition, NMR studies confirm in situ generation of normal N‐heterocyclic carbenes from the C‐2 position of imidazol‐2‐ylidene ring. The mercury poisoning test was also performed to ascertain the nature of catalytically active palladium species. Aerobic conditions, low catalytic loading (0.5 mol%), shorter reaction times, broad functional group tolerance and good to excellent isolated yields are some of the significant features of the novel catalytic systems described here. Copyright © 2016 John Wiley & Sons, Ltd.     

单轴拉伸对Nafion 结构及性能的影响

²H NMR 和PFG-NMR 用于研究拉伸过程中Nafion 结构的改变以及对溶剂分子运动性质的影响．²H 谱表明单轴拉伸Nafion 膜在拉伸比率较低情况下（L < 5），通道排列取向程度随着拉伸比率变大而增大，同时扩散实验表明水分子的运动能力也得到增强，表明取向化的通道网络有助于增强材料取向方向质子的导电能力，可以用于提高质子膜材料性能．在取向达到最大值后（L≥5）继续拉伸，膜内水分子的移动能力相比略有降低．溶胀实验表明取向膜的溶胀行为呈各向异性,拉伸作用致使膜内通道沿拉伸方向取向排列，通道的取向效应使得其在垂直拉伸方向（Y）和膜厚度方向（Z）溶胀更为显著．拉伸Nafion 膜对甲醇的吸附能力随着拉伸比率的增加而增强，同时甲醇的扩散数据显示，甲醇的运动能力在该通道网络中也随着拉伸比率的变大而不断增强，甲醇燃料在该类质子膜内的渗透效
应得以增强，不利于其在直接甲醇燃料电池中的应用．     

Application of electromagnetic processing for development of high-performance sintered powder metal parts

Electromagnetic processing was used to study the effects of electro-magneto forming on the dimensional control and thermal stability of sintered powder metal (PM) parts. The investigation was carried out on sinter-hardened, low chromium-molybdenum bainitic steel. The results show an increase in the microhardness of about 14% for the electromagnetic processed parts compared to the as-sintered parts. This was attributed to the 2% increase in the density, 17% and 29% reduction in the volume fraction of porosity and width of the bainitic lath, respectively, due to the electromagnetic processing. Dimensional characterization was carried out using a vertically aligned push-rod dilatometer. After four thermal cycles of heating and cooling, at a controlled rate of 5 °C/min to 1000 °C, the electromagnetic processed parts exhibited reduced dimensional change of about 44% lower than for the as-sintered parts. This is significantly important for applications that demand high dimensional tolerance and performance, especially at elevated temperatures.     

State space approach to magnetohydrodynamic flow of perfectly conducting micropolar fluid with stretch

In this work we introduce a model of the boundary layer equations for a perfect conducting micropolar fluid with stretch, bounded by an infinite vertical flat plane surface of a constant temperature. This model is applied to study the effects of free convection currents on the flow of the fluid in the presence of a constant magnetic field. The state space technique is adopted for the solution of a one‐dimensional problem for any set of boundary conditions. The resulting formulation together with the Laplace transform techniques are applied to a thermal shock problem. The inversion of the Laplace transforms is carried out using a numerical approach. Numerical results are given and illustrated graphically for the problem. Copyright © 2011 John Wiley & Sons, Ltd.     

Preparation and Characterization of Styrene/Butyl Acrylate Emulsifier-Free Latex with 2-Acrylamido-2-Methyl Propane Sulfonic Acid as a Reactive Emulsifier

A kind of emulsifier-free latex (FL) was successfully synthesized from styrene (St) and butyl acrylate (BA) with 2-acrylamido-2-methyl propane sulfonic acid (AMPS) as a reactive emulsifier. The particle size of latex particles, stability against electrolytes, minimum film forming temperature (MFT) and water contact angle (CA) were evaluated and compared with a conventional latex (CL). Test results show that FL has larger particle size, better stability against electrolytes and lower MFT value compared with CL; higher AMPS content leads to smaller particle size and smaller water CA.     

A Raman technique applicable for the analysis of the working principle of promoters and inhibitors of gas hydrate formation

We report a Raman technique applicable for the in situ analysis of the development of hydrogen bonds in the liquid water‐rich phase just before the onset of gas hydrate formation. Herewith, the phase transition as well as the working principle of hydrate formation inhibitors and promoters can be analyzed. © 2015 The Authors. Journal of Raman Spectroscopy published by John Wiley & Sons Ltd.     

Infrared and NMR Spectroscopic Fingerprints of the Asymmetric H7+O3 Complex in Solution

Infrared (IR) absorption in the 1000–3700 cm⁻¹ range and ¹H NMR spectroscopy reveal the existence of an asymmetric protonated water trimer, H₇⁺O_3, in acetonitrile. The core H₇⁺O₃ motif persists in larger protonated water clusters in acetonitrile up to at least 8 water molecules. Quantum mechanics/molecular mechanics (QM/MM) molecular dynamics (MD) simulations reveal irreversible proton transport promoted by propagating the asymmetric H₇⁺O₃ structure in solution. The QM/MM calculations allow for the successful simulation of the measured IR absorption spectra of H₇⁺O₃ in the OH stretch region, which reaffirms the assignment of the H₇⁺O₃ spectra to a hybrid-complex structure: a protonated water dimer strongly hydrogen-bonded to a third water molecule with the proton exchanging between the two possible shared-proton Zundel-like centers. The H₇⁺O₃ structure lends itself to promoting irreversible proton transport in presence of even one additional water molecule. We demonstrate how continuously evolving H₇⁺O₃ structures may support proton transport within larger water solvates.     

三功能策略设计制备具有优异低温抗积碳性能的Ni-CeO2@SiO2催化剂催化甲烷干重整反应

随着全球人为温室气体排放量(主要是甲烷和二氧化碳)的增加,全球变暖的趋势逐渐增加,因此,迫切需要通过各种技术来捕获和利用这些温室气体.甲烷干气重整反应(DRM)可以有效地将甲烷和二氧化碳这两种资源丰富、价格低廉的温室气体转化为高附加值化学品,减少它们向大气排放.尽管DRM工艺的应用具有许多优势,但是反应期间碳沉积和活性组分的烧结是阻碍其工业应用的两个主要原因.这些碳沉积物可能覆盖活性中心或阻塞催化剂的孔道,从而导致催化剂活性降低.镍基催化剂因其价格低廉、初始活性高和资源丰富而得到广泛的应用.但应用于DRM反应的Ni基催化剂在反应中容易烧结和积碳,导致催化剂迅速失活.为解决上述问题,本文从三功能策略角度出发,即SiO2壳层的限域作用和Ni-Ce之间的协同作用以及CeO2的消除积碳作用,采用原位一锅法设计合成了一种限域型Ni-CeO2核壳结构催化剂(Ni-CeO2@SiO2).通过X射线衍射、透射电子显微镜、能量色散X射线光谱、N2吸附/脱附、氢气程序升温还原和脱附、氧气程序升温脱附、拉曼光谱、热重分析和原位漫反射红外傅里叶变换光谱测试对催化剂进行了系统的表征,来揭示催化剂的理化性质和反应机理.催化剂应用于甲烷干气重整反应结果表明,在温度区间为550～800℃时,与传统浸渍法合成的催化剂相比,Ni-CeO2@SiO2催化剂具有更高的活性.高温800℃下的稳定性测试结果显示,传统浸渍法合成的催化剂在反应20 h后就出现了大量的积碳且活性下降明显;而Ni-CeO2@SiO2催化剂在800℃下反应100 h后未检测到积碳,并且催化剂中的Ni纳米颗粒的平均粒径从5.01 nm仅增长到5.77 nm,表现出很好的高温抗积碳和耐烧结性能.值得注意的是,Ni-CeO2@SiO2催化剂在低温600℃(形成碳沉积的最可能温度区域)下反应20h后也未检测到积碳的形成,表现出催化剂良好的低温稳定性和抗积碳性能.这可能归因于对Ni-CeO2@SiO2催化剂的三功能作用,即多孔二氧化硅壳层的限域作用、Ni与CeO2之间强的金属-金属氧化物相互作用以及具有丰富活性氧物种CeO2的消除积碳的作用.通过原位漫反射红外傅里叶变换光谱测试来探究反应机理.结果 表明,DRM反应在Ni-CeO2@SiO2催化剂上遵循L-H机理,添加CeO2可以消除碳沉积并促进CO2活化.该三功能策略为设计其他应用于DRM的高性能催化剂提供了指导,有望加快该工艺的工业化.     

飞秒激光冲击AZ31B镁合金过程的数值模拟

采用有限元分析法对飞秒激光冲击AZ31B镁合金进行数值模拟,研究了激光冲击处理对镁合金变形过程的影响,分析了单脉冲激光冲击下材料内部的位移、动能、应力和应变的分布情况,得到了材料的瞬态速度和应变率变化过程.仿真结果表明,单脉冲飞秒激光冲击镁合金产生的塑性变形,可在材料表面形成微米级凹坑,中心点处最大位移为34μm,最大变形速度390m/s;在冲击初期,材料表面的应力和应变主要分布在冲击区域中心节点和边缘附近,并且得到镁合金的最大应力和最大应变率分别为955 MPa和1.8×106 s-1.研究结果能够为深入分析飞秒激光与镁合金作用时材料变形参量的变化规律提供数值理论依据.