Nb(iPrNPMe2)3Fe–PMe3: A potential high reactivity heterobimetallic catalyst for acetylene cycloadditions

Alkynes cycloaddition reactions are powerful tools for constructing cyclic molecules with optimal atom efficiency, but these reactions cannot proceed at ambient temperature without transition-metal catalysts. In this work, a heterobimetallic complex featuring an Nb–Fe triple bond, Nb(ⁱPrNPMe₂)₃Fe–PMe₃, has been evaluated as the potential catalyst for acetylene cycloaddition, using density functional theory. The calculated results show that the singlet-state (i.e. ground-state) Nb(ⁱPrNPMe₂)₃Fe–PMe₃ can be applied to benzene synthesis, but is not suitable for cyclobutadiene. Benzene can be obtained easily at room temperature and is the unique product on the singlet potential surface. The irradiation of infrared-red light can drive the excitation of singlet Nb(ⁱPrNPMe₂)₃Fe–PMe₃ to its triplet state. Both benzene and cyclobutadiene can be formed on the triplet reaction potential surface due to their low energy barriers. Therefore, Nb(ⁱPrNPMe₂)₃Fe–PMe₃ is a potential high reactivity heterobimetallic catalyst for the cyclotrimerization of alkynes. In the reaction process, the catalytic active site of Nb(ⁱPrNPMe₂)₃Fe–PMe₃ moves from niobium to iron.     

General Formation of Macro-/Mesoporous Nanoshells from Interfacial Assembly of Irregular Mesostructured Nanounits

Mesoporous core–shell nanostructures with controllable ultra-large open channels in their nanoshells are of great interest. However, soft template-directed cooperative assembly to mesoporous nanoshells with highly accessible pores larger than 30 nm, or even above 50 nm into macroporous range, remains a significant challenge. Herein we report a general approach for precisely tailored coating of hierarchically macro-/mesoporous polymer and carbon shells, possessing highly accessible radial channels with extremely wide pore size distribution from ca. 10 nm to ca. 200 nm, on diverse functional materials. This strategy creates opportunities to tailor the interfacial assembly of irregular mesostructured nanounits on core materials and generate various core–shell nanomaterials with controllable pore architectures. The obtained Fe,N-doped macro-/mesoporous carbon nanoshells show enhanced electrochemical performance for the oxygen reduction reaction in alkaline condition.     

离心力场作用下多孔介质中强制对流换热的研究

对离心流化床中空气通过多孔物料层的强制对流换热进行了理论和实验研究。获得了气流和物料间强制对流换热的准则关联式。研究结果表明,在气流速度和温度梯度方向一致的条件下,强制对流换热比通常的边界层强制对流换热有所强化,其换热的准则关联式具有 Nu=CRePr的线性形式。从而验证了改变气流方向和热流密度矢量之间夹角可以强化换热的这一强化传热新原理。     

Studying the process of ionization of hydrogen in conditions of its forced delivery to a porous nickel oxide electrode

The hydrogen ionization process is studied experimentally on an industrial sintered nickel oxide electrode in models of sealed nickel-metal hydride batteries. It is shown that the hydrogen ionization rates that are reached during overcharge by high current densities in conditions of forced gas delivery into the electrode pores (up to 40 mA cm^?2) exceed the self-discharge rate of a nickel-hydrogen battery by two orders of magnitude. Up to 70% of hydrogen delivered into the compact assembly block undergoes ionization during forced charge of models of sealed nickel-metal hydride batteries with a closed hydrogen cycle. Two independent methods (potentiostatic and manometric) are used to determine the relationship between rates of hydrogen ionization with the degree of the electrode filling with gas and perform estimation of the process intensity at a unit reaction surface. It is established that, in conditions of forced gas delivery, practically all the hydrogen oxidation current is generated at the surface of the nickel oxide electrode beneath thin films of an electrolyte solution at the rate of 4–5 mA cm^?2. It is shown that the hydrogen oxidation rate on a nickel oxide electrode filled in part by gas is independent of the electrode potential, probably because of a tangible contribution made by diffusion limitations to the overall hampering of the process.     

Mathematical modeling of flows through inelastic porous solids

We propose a framework, based on classical mixture theory, to describe the isothermal flow of an incompressible fluid through a deformable inelastic porous solid. The modeling of the behavior of the inelastic solid takes into account changes in the elastic response due to evolution in the microstructure of the material. We apply the model to a compression layer problem. The mathematical problem generated by the model is a free boundary problem.     

a-C:F薄膜的热稳定性与光学带隙的关联

以CF4和C6H6的混合气体作为气源,在微波电子回旋共振化学气相沉积(ECRCVD)装置中制备了氟化非晶碳薄膜(aC:F),并在N2气氛中作了退火处理以考察其热稳定性.通过傅里叶变换红外吸收谱和紫外可见光谱获得了薄膜中CC双键的相对含量和光学带隙,发现膜中CC键含量与光学带隙之间存在着密切的关联,在高微波功率下沉积的氟化非晶碳膜具有低的光学带隙和较好的热稳定性. 关键词： 氟化非晶碳膜 光学带隙 退火温度 热稳定性     

生长温度对碳纳米管阴极场发射性能的影响

碳纳米管(Carbon Nanotubes,CNTs)场发射平面显示器(Field Emission Display,FED)与其他显示器比较显示了其独特优点,被认为是未来理想的平面显示器之一。碳纳米管阴极作为器件的核心部分,其性能的好坏直接影响显示器的性能。针对30~60英寸(76.2~152.4cm)大屏幕显示器所用的厚膜工艺,即采用丝网印刷法制备了碳纳米管阴极阵列,研究了化学气相沉积法在不同温度下生长的CNTs的场发射电流-电压特性,找到了适合FED用碳纳米管的最佳生长温度。结果表明生长温度越高(750℃),CNTs场发射性能越好。并用荧光粉阳极测试这些CNTs的场发射发光显示效果,验证了上述结论。     

A study on the electrical conductivity of multi-walled carbon nanotube aqueous solution

The electrical conductivity was investigated for multi-walled carbon nanotubes (MWNTs) dissolved in chloroform and toluene, respectively. The electrical conductivity remarkably increased with increase in the content of MWNTs, which is in accordance with Archie's equation . Furthermore, a hypothesis of the electronic transport process was proposed to explain the difference between the solution and the solid compound. In addition, the temperature dependence of the electrical conductivity shows that log σ vs. 1/T exist in a good linear relationship. The activation energy of the electrical conductivity decreased with increase in concentration and an inflexion was observed at 60 °C in MWNT/toluene solution.     

Theoretical Study on the Reaction Mechanism between Dichlorocarbene and Armchair Single-walled Carbon Nanotubes

1 INTRODUCTION Carbon nanotubes have many potential applica- tions due to their unique structures and properties[1～4]. Physicists have been studying their electrical, me- chanical and other properties since their discove- ries[5, 6]. Recently, chemists are interested in carbon nanotubes because their properties can be altered by chemical functionalization[7～14], and these functiona- lized nanotubes can undergo further chemical trea- tment. So the potential application range of such na- …     

Non‐empirical calculations of NMR indirect carbon–carbon coupling constants. Part 4: Bicycloalkanes

A systematic study of the one‐bond and long‐range J(C,C), J(C,H) and J(H,H) in the series of nine bicycloalkanes was performed at the SOPPA level with special emphasis on the coupling transmission mechanisms at bridgeheads. Many unknown couplings were predicted with high reliability. Further refinement of SOPPA computational scheme adjusted for better performance was carried out using bicyclo[1.1.1]pentane as a benchmark to investigate the influence of geometry, basis set and electronic correlation. The calculations performed demonstrated that classical ab initio SOPPA applied with the locally dense Dunning's sets augmented with inner core s‐functions used for coupled carbons and Sauer's sets augmented with tight s‐functions used for coupled hydrogens performs perfectly well in reproducing experimental values of different types of coupling constants (the estimated reliability is ca 1–2 Hz) in relatively large organic molecules of up to 11 carbon atoms. Additive coupling increments were derived for J(C,C), J(C,H) and J(H,H) based on the calculated values of coupling constants within SOPPA in the model bicycloalkanes, in reasonably good agreement with the known values obtained earlier on pure empirical grounds. Most of the bridgehead couplings in all but one bicycloalkane appeared to be essentially additive within ca 2–3 Hz while bicyclo[1.1.1]pentane demonstrated dramatic non‐additivity of ?14.5 Hz for J(C,C), +16.6 Hz for J(H,H) and ?5.5 Hz for J(C,H), in line with previous findings. Non‐additivity effects in the latter compound established at the SOPPA level should be attributed to the through‐space non‐bonded interactions at bridgeheads due to the essential overlapping of the bridgehead rear lobes which provides an additional and effective non‐bonding coupling path for the bridgehead carbons and their protons in the bicyclopentane framework. Copyright © 2003 John Wiley & Sons, Ltd.