高稳定性的氮掺杂氧化钽光催化甲醇C−H活化和直接C−C偶联制乙二醇

乙二醇是非常重要的基础化学品,不仅可以作为合成聚合物(如聚对苯二甲酸乙二醇酯)的重要单体,也可以用作防冻剂和燃料添加剂等,具有广泛的用途.乙二醇的年产量超过2500万吨,目前主要的工业合成路线是由石油衍生的乙烯通过环氧化制环氧乙烷,环氧乙烷再水解制乙二醇.甲醇是一种清洁的平台化合物,不仅可以由天然气和煤炭通过传统的合成气过程生产,也可以由生物质和CO2直接合成.直接以甲醇为原料是合成乙二醇的理想过程,但目前热催化还未实现该过程.通过太阳能驱动的C?H活化和C?C偶联过程,可以实现甲醇直接偶联制乙二醇的理想反应过程.光催化甲醇制乙二醇可以在十分温和的条件下进行,目前已报道的甲醇制乙二醇光催化剂均为硫化物半导体材料,如CdS,ZnS和Zn2In2S5,但硫化物存在的光腐蚀和毒性等问题迫使我们去发展一种更加稳定和环境友好的光催化剂.氧化物基半导体材料,如Ta2O5,TiO2,ZnO和WO3等,是一类相对硫化物半导体材料更加稳定的光催化材料,然而目前还没有氧化物基半导体光催化剂用于光催化甲醇制乙二醇的报道.本文率先将金属氧化物光催化剂Ta2O5,用于甲醇制乙二醇的光催化反应,实现了乙二醇的选择性合成.在单纯的Ta2O5催化剂上,乙二醇选择性可达73％.Ta2O5十分独特,可以实现甲醇的光催化C?C偶联制乙二醇,而其他金属氧化物光催化剂(如TiO2,ZnO,WO3和Nb2O5)光催化转化甲醇只生成甲醛和甲酸等C1产物.进一步通过简单、方便的氨气焙烧法,制备了一系列不同氮掺杂量的氧化钽(N-Ta2O5)催化剂.在未经助催化剂修饰的氮含量为2.3％的2％N-Ta2O5光催化剂上,乙二醇选择性为71％,生成速率可达4.0 mmol gcat?1 h?1,约为Ta2O5的9倍,同时显著高于已报道的未经助催化剂修饰的CdS催化剂性能.通过光电流、表面光电压谱和理论计算等方法系统地研究了氮掺杂氧化钽具有高的光催化甲醇制乙二醇性能的重要原因,发现氮掺杂氧化钽高的电荷分离能力是决定其具有高活性的关键因素.另一方面,氮掺杂氧化钽表现出了非常高的反应稳定性,在超过160 h的循环测试过程中,乙二醇的生成速率基本保持不变,这是目前已报道的金属硫化物光催化剂所未能实现的.在长达60 h的反应过程中,未经助催化剂修饰的2％N-Ta2O5催化剂上乙二醇生成量基本随时间线性增长,收率可达3.6％.进一步研究发现,钽基半导体材料(Ta2O5和N-Ta2O5)可以在保持甲醇羟基不变的情况下优先活化甲醇C?H键,生成羟甲基自由基(?CH2OH),随后羟甲基自由基经C?C偶联生成乙二醇.钽基半导体光催化剂是一种环境友好且十分稳定的甲醇光催化偶联制乙二醇的优异催化剂,未来基于该类催化剂不仅有希望发展出更加高效、稳定的甲醇制乙二醇光催化剂,还有希望为更广的羟基存在下的C?H键选择性活化反应过程设计高效稳定的催化剂提供借鉴和指导.     

Kinetics for the reaction of methine proton of an unsymmetrical tetradentate Schiff base complex of nickel(II) with N-chlorosuccinimide

The substitution reaction of the methine proton of an unsymmetrical tetradentate Schiff base complex of nickel(II) with N-chlorosuccinimide was kinetically studied in a dichloromethane solution. While the rate of chlorination was decreased by the addition of acetone or ether, the rate was significantly increased by the addition of ethanol. The rate of bromination was faster than that of chlorination. A four-centred intermediate was proposed for the halogenation reaction of the Schiff base nickel(II) complex.     

The reaction of perfluorobicyclic ethers and perfluorospiro-ethers with anhydrous aluminum chloride

Perfluorobicyclic ethers and perfluorospiroethers, all containing an oxolane skeleton, were treated with AlCl₃ in a heterogeneous manner to give the corresponding α,α,α′-trichlorinated and α,α-dichlorinated products, respectively. From perfluoroacetal compounds, for example, perfluoro(8-methoxy-7-oxabicyclo- [4.3.0]nonane), mono- and di-chlorinated products, i.e. perfluoro- (8-chloro-8-methoxy-7-oxabicyclo[4.3.0]nonane) and perfluoro- (8,8-dichloro-7-oxabicyclo[4.3.0]nonane) were obtained in good yields. The action of fuming sulfuric acid on these polychlorinated products led to the formation of the corresponding lactones. Perfluoro(6-chloro-7-oxa-8-oxobicyclo[4.3.0]nonane) was treated with (CH₃)₂NLi to give N,N-dimethylundecafluoro-2-oxocyclohexyl- acetamide.     

Development of a new radiation detector utilizing CNTs as anodes

A new gas-multiplication radiation detector utilizing CNTs as anodes is proposed. A very compact detector with good spatial and temporal resolutions might be built. The designing and development of a prototype detector is described. Argon gas or liquid is adopted as radiation-converting medium. The detector body can be evacuated and cooled down to liquid nitrogen temperature. Silicon wafers on which single-wall CNTs are grown are used as the detector anode.     

Synthesis and properties of hexakis(6-octyl-2-azulenyl)benzene as a multielectron redox system with liquid crystalline behavior

[structure: see text] This paper describes the cyclotrimerization reaction of di(2-azulenyl)acetylenes (2a,b) catalyzed by Co2(CO)8 to produce hexa(2-azulenyl)benzene derivatives (1a,b). The cyclooligomerization of 2a and 2b utilizing CpCo(CO)2 as a catalyst produced (eta5-cyclopentadienyl)[tetra(2-azulenyl)cyclobutadiene]cobalt complexes (3a,b). The redox behavior of hexakis(6-octyl-2-azulenyl)benzene (1b), bis(6-octyl-2-azulenyl)acetylene (2b), and the cobalt complexes 3a and 3b along with 6-octyl-2-phenylazulene (19) was examined by cyclic voltammetry (CV). The reduction of compound 1b exhibited multiple-electron transfers in one step upon CV with a reduction potential similar to that of compound 19. However, the CVs of compounds 2b, 3a, and 3b were characterized by stepwise waves because of the reduction of each azulene ring. The mesomorphic behaviors of 1b, 2b, and 19 were also studied by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction (XRD) techniques. A new series of azulene derivatives, 1b, 2b, and 19, substituted by a long alkyl chain at the 6-position shows mesomorphism with crystalline polymorphs. Compound 1b showed a large temperature range of hexagonal columnar mesophases (Col(ho)) from 115.5 to 199.9 degrees C. Compound 2b has rectangular columnar (Col(ro)), smectic E (S(E)), and nematic (N) mesophases. Compound 19 exhibited an S(E) mesophase.     

Atomic correlation between adjacent graphene layers in double-wall carbon nanotubes

Atomic correlation between adjacent graphene layers was elucidated for double-wall carbon nanotubes (DWNTs) through a chiral index assignment of two nested nanotubes by high-resolution transmission electron microscopy. Our analysis provides a rather constant diameter difference close to 0.75 nm but no chiral angle correlation between the constituent nanotubes in the concentric DWNTs. The local atomic correlation as a commensurate graphene stacking was repeatedly found in eccentric DWNTs and circumscribed nanotubes, which should lead to elastic deformation and bundling of nanotubes.     

Giant cluster coexistence in doped manganites and other compounds

Computational studies of models for manganese oxides show the generation of large coexisting metallic and insulating clusters with equal electronic density, in agreement with the recently discovered micrometer-sized inhomogeneities in manganites. The clusters are induced by disorder on exchange and hopping amplitudes near first-order transitions of the nondisordered strongly coupled system. The random-field Ising model illustrates the qualitative aspects of our results. Percolative characteristics are natural in this context. The conclusions are general and apply to a variety of compounds.     

The optimal repair-time limit replacement policy with imperfect repair: Lorenz transform approach

In this paper, we consider a simple repair-time limit replacement problem with imperfect repair, and focus on the problem of determining the optimal repair-time limit which minimizes the expected cost per unit time in the steady-state. Applying the Lorenz transform, we develop a nonparametric method to estimate the optimal repair-time limit from the empirical repair-time data. Numerical examples are considered to calculate the optimal policy and to examine the asymptotic properties of the estimator.     

Crystal orientation in a semicrystalline polymer in relation to deformation of polymer spherulites. II. Orientation distribution function of crystallites within crystal lamella as a function of lamellar orientation

A model relating crystal orientation in a semicrystalline polymer to the deformation of polymer spherulites is proposed. The distribution function for orientation of crystallites within crystal lamellae is assumed to be a function of lamellar orientation. In addition to the orientation of crystal lamellae in affine fashion, several parameters are introduced to characterize the untwisting of the crystal lamellae and the four different types of orientations of the crystallites within the crystal lamellae in the undeformed and deformed states of the spherulite. The model was tested by experiments in uniaxial stretching of a low-density polyethylene. The theoretical distributions of orientation of given reciprocal lattice vectors of the crystallites, such as the reciprocal lattice vectors of the (110) and (200) crystal planes, are compared with the results of x-ray diffraction experiments. It was found that the most important factors in fitting the model to experimental results are: (a) the fraction of crystallites having random orientation within lamella and, in turn, representing the degree of imperfection of the lamella in the undeformed state; (b) the ease of transition of crystal orientation within lamella from b-axis orientation parallel to the lamellar axis to two types of c-axis orientations (type C_a and type C_r) parallel to the stretching direction; and (c) the fraction of crystallites having orientation in type C_r (unfolding mechanism) rather than type C_a (rotation mechanism).     

Investigation of stability of (Ge,Sn)-(S,or Se)42 cluster vibrational spectra

The insistent two mode type behavior of the A₁ and high frequency F₂ bands in the tin contained glasses is reproduced by our vibrational calculations based on the outrigger-raft with some modifications. High pressure Raman spectra suggest an instability of the tin tetrahedral bonding. Comparative study of glassy and crystalline Ge(Se, or S)₂ by high pressure Raman scattering gives important informations about the strain field and the topological order in the glasses.