γ-Mo2N催化剂上H2及NO吸附性质的TPD-MS研究

采用TPD-MS方法研究了H2及NO在γ-Mo2N上的吸附状况．单独的H2-TPD结果表明,当H2在673K吸附时,在443K、573K及723K得到了三个H2脱附峰,表明γ-Mo2N上有三种不同能量的H2吸附位．NO－TPD结果表明,NO吸附后亦有三个脱附峰（383K、493K、543K）,对应着γ-Mo2N上三种不同能量的NO吸附位：低、中、高能吸附位．NO既可以以解离状态,又可以以一种NO三聚态（dimerordinitrosyl）的形式吸附在γ－Mo2N上,这些吸附物种在脱附过程中产生大量的N2及少量的N2O.对比NO吸附在不同处理条件的γ-Mo2N上的TPD结果可知,NO是吸附在γ-Mo2N上的MO的配位不饱和中心上,这些吸附中心既可通过还原催化剂,又可通过在773K抽空钝化态的γ－Mo2N而产生,H2和NO共吸附的结果表明,预吸附H2再吸附NO后,H2和NO的脱附量均大大减少,且只有两个脱附峰出现.NO只在363K及493K出现两个脱附峰,表明预吸附氢占据了NO的强吸附位,且NO很难取代它,从而使NO只能吸附在能量较低的吸附位上;而H2只在523K及723K出现两个脱附峰,且伴随着H2的脱出有N2和H2O的产生,表明在γ－Mo2N上NO可能与预吸附氢形成了一种复合相MoHx（NO）y,它在脱附时分解为H2、N2及H2O.     

Potentiometric titration of chlorine and its oxy compounds in water

Potentiometric titrations at constant current with identical platinum electrodes are applied to mixtures of chlorine, chlorine dioxide and chlorite. The procedure is compared with the common amperometric method. Chlorine can be titrated with phenylarsine oxide at pH 7 even in mixtures with chlorine dioxide and chlorite, and three-component mixtures can be resolved by titrations at pH 2 and 7 with and without iodide addition. The behavior of chlorine and chlorite mixtures can be characterized by appropriate titrations.     

A critique of lifetime prediction of polymers by thermal analysis

Attempts are made to use kinetics parameters from thermal decomposition experiments at high temperatures to predict service lifetimes of polymeric materials at lower temperatures. However, besides the obvious measurement and extrapolation errors (which can be considerable), there are two fundamental reasons why quantitative long range extrapolations can not be made for complex condensed phase systems. They are: 1) Arrhenius kinetics parameters can not be extrapolated through phase transitions or softening temperatures; 2) Arrhenius kinetics parameters can not be extrapolated through the ceiling temperature region. Satisfactory lifetime prediction methods can be developed only after a thorough analysis of the causes of service failure. A real method has been taken from literature to illustrate the correct procedures. This paper is, in part, based on the Honorary Guest Lecture given at the Sixth Seminar in Memory of Stanislaus Bretsznajder [1].     

石英的顺磁中心在电子自旋共振测年中的特性及应用

沉积物的电子自旋共振测年是利用石英矿物中的顺磁中心浓度确定总辐射能量,进而推定石英矿物的埋藏年代。石英中可用于测年的顺磁中心包括E′心、Al心、Ti心和Ge心。E′心需要经过热活化后才能测年。Al心是一种电子空穴心,在低温下可观测到较强的信号值。光照可以使Al心漂白,但有残留值存在。Ti心、Ge心都是电子中心,Ti心在低温测试中可见,信号微弱。Ge心光晒退最敏感,在常温观测中可见。不同顺磁中心的形成机理不同,导致它们具有不同的特性,适用于不同沉积环境中的样品测年,在冰碛物中Ge心测年更具有可行性。电子自旋共振测试时降低温度可使信号增强,Ti心在10 K和15 K时信号强度最大;Al心在20 K时信号最强;Ge心在200 K时信号明显增强。在电子自旋共振测年中可根据不同顺磁中心信号强度的变化调整测试温度获得信号的最优值。在以后的电子自旋共振(ESR)测试中可以选取信号最强时的测试温度进行测试,以增强微弱信号的信噪比,有利于对复杂的信号形态的分辨确定,提高对信号强度定量的准确性。     

Determination of lanthanum with n-benzoyl-n-phenylhydroxylamine

N-Benzoyl-N-phenylhydroxylamine is proposed for the gravimetric determination of lanthanum, at pH 6.4–7.2. The precipitates can be weighed directly or ignited to the oxide. By suitable pH adjustment, many metals can be separated from lanthanum, which can then be determined in the filtrates. Interferences of Ni, Cu, Zn and Fe(II) are masked with cyanide. About 99.5% of cerium can be separated from lanthanum by precipitating cerium(IV) at pH 4.8–5.2.     

Highly stereoselective syntheses of syn- and anti-1,2-amino alcohols

The reduction of N-protected amino ketones can be carried stereoselectively to produce either the syn- or anti-amino alcohol diastereomer. Carbamate-protected amino ketones can be reduced predictably and selectively to anti-amino alcohols with LiAlH(O-t-Bu)3 in ethanol at -78 degrees C. N-Trityl-protected amino ketones can be reduced selectively to syn-amino alcohols with LiAlH(O-t-Bu)3 in THF at -5 degrees C.     

温和条件下甲醛在 Pt/TiO2 上催化氧化反应的原位漫反射红外光谱研究

 采用原位漫反射红外光谱研究了温和条件下 1%Pt/TiO2 催化剂上甲醛的吸附和氧化反应, 并对催化剂的失活进行了分析. 结果表明, Pt/TiO2 催化剂在室温条件下即可将甲醛氧化成 H2O 和 CO2, 100 oC 以下甲酸根的分解为决速步骤, 低温下催化剂失活是由于表面未能及时分解的甲酸根占据了催化剂的活性位, 升温至 100 oC 即可将甲酸根完全分解并恢复催化剂的活性.     

Solvent-exfoliated graphene at extremely high concentration

We describe three related methods to disperse graphene in solvents with concentrations from 2 to 63 mg/mL. Simply sonicating graphite in N-methyl-2-pyrrolidinone, followed by centrifugation, gives dispersed graphene at concentrations of up to 2 mg/mL. Filtration of a sonicated but uncentrifuged dispersion gives a partially exfoliated powder that can be redispersed at concentrations of up to 20 mg/mL. However, this process can be significantly improved by removing any unexfolaited graphite from the starting dispersion by centrifugation. The centrifuged dispersion can be filtered to give a powder of exfoliated few-layer graphene. This powder can be redispersed at concentrations of at least 63 mg/mL. The dispersed flakes are ~1 μm long and ~3 to 4 layers thick on average. Although some sedimentation occurs, ~26-28 mg/mL of the dispersed graphene appears to be indefinitely stable.     

Langmuir monolayers as models to study processes at membrane surfaces

The use of new sophisticated and highly surface sensitive techniques as synchrotron based X-ray scattering techniques and in-house infrared reflection absorption spectroscopy (IRRAS) has revolutionized the monolayer research. Not only the determination of monolayer structures but also interactions between amphiphilic monolayers at the soft air/liquid interface and molecules dissolved in the subphase are important for many areas in material and life sciences. Monolayers are convenient quasi-two-dimensional model systems. This review focuses on interactions between amphiphilic molecules in binary and ternary mixtures as well as on interfacial interactions with interesting biomolecules dissolved in the subphase. The phase state of monolayers can be easily triggered at constant temperature by increasing the packing density of the lipids by compression. Simultaneously the monolayer structure changes are followed in situ by grazing incidence X-ray diffraction or IRRAS. The interactions can be indirectly determined by the observed structure changes. Additionally, the yield of enzymatic reaction can be quantitatively determined, secondary structures of peptides and proteins can be measured and compared with those observed in bulk. In this way, the influence of a confinement on the structural properties of biomolecules can be determined. The adsorption of DNA can be quantified as well as the competing adsorption of ions at charged interfaces. The influence of modified nanoparticles on model membranes can be clearly determined. In this review, the relevance and utility of Langmuir monolayers as suitable models to study physical and chemical interactions at membrane surfaces are clearly demonstrated.     

Determination and differentiation of nitrilotriacetic acid and ethylenediaminetetra-acetic acid

Ethylenediaminetetra-acetic acid (EDTA) and nitrilotri-acetic acid (NTA) can be differentiated and determined by titration with metal ions to visual metallochromic dye end-points. EDTA can be determined without interference from NTA, either by titrating with copper(II) at pH 5 using PAN indicator, or by titrating with iron(III) at pH 6 and 70 degrees using Tiron indicator. The total chelating power (EDTA + NTA) can be determined either by titrating with lead(II) at pH 4.4 using dithizone indicator, or by titrating with iron(III) at pH 3.5 using Tiron indicator ; NTA is determined by difference. The lowest concentration at which NTA can be determined in EDTA by titration to the iron(III)-Tiron end-point is about 1 wt.%. The apparent stability constants of the iron(III)-Tiron complexes under the conditions of the titration at pH 3.5 and pH 6 have been determined using the method of continuous variations.     

原位红外光谱研究Ni/Al2O3催化剂上CO的吸附态:Ⅰ.CO的倒式吸附态

CO在过渡金属上的吸附方式一般认为可分成三类:线式吸附态,桥式吸附态和多重键吸附态.这些吸附态的C—O伸缩振动具有红外活性,共振动频率分别位于～2050,～1950和～1700cm~(-1).但也有人认为CO在过渡金属表面上可能会形成倒式吸附态,即C—O键向表面倾斜,甚至平行于表面.例如,Dijk等曾推测在Ni/SiO_2催化剂上CO可能形成倒式双点吸附态(即C,O原子同时与表面成键).Krasser等用喇曼光谱研究CO在Ni/SiO_2上的吸附态时发现在330cm~(-1)处有一喇曼峰,认为这个峰可能来自倒式     

Modulated surface vibrational spectroscopy at the electrode—solution interface

Infrared spectroelectrochemistry can be used to examine reactions occurring at the electrode—solution interface. This vibrational probe can be applied to study the structure and orientation of molecules and the dynamics of adsorption—desorption processes at the electrode surface. The technique can reveal valuable information about the mechanisms and kinetics of surface reactions.     

Novel acetoxylation and C-C coupling reactions at unactivated positions in alpha-amino acid derivatives

[Structure: see text] Under special conditions, N-phthaloyl-alpha-amino acid amides of 8-aminoquinoline can be either acetoxylated or arylated selectively at the beta-carbon. In certain cases, arylation can be effected at the gamma-carbon.     

The Use of Light in the Study of Interfacial Electrochemical Reactions

Spectroscopic analysis techniques have become particularly important in the study of interfacial electrochemical processes since it has become possible to increase their sensitivity to the extent where changes occurring in the absorption of light by fractions of monolayers can be detected. At the same time the development of new techniques in surface physics, though most of these can only be used in ultra-high vacuum, has also had a considerable influence on electrochemistry since it has enabled studies to be carried out on electrodes after transfer to UHV. The availability of well-defined semiconductors in which photocurrents can be generated by the absorption of light has led to the development of photoelectrochemical methods that can be used for the study of electrode reactions at semiconductors or at metal surfaces which are covered with a semiconducting film. Finally, it has been observed during the study of semiconductor electrodes that redox reactions at an electrode can result in the generation of luminescence. This, in turn, can lead to important information on the mechanism of the charge transfer process. These recent developments are reviewed in the present article.     

Sizes of pentagonal clusters in fullerenes

Stability and chemistry, both exohedral and endohedral, of fullerenes are critically dependent on the distribution of their obligatory 12 pentagonal faces. It is well known that there are infinitely many IPR-fullerenes and that the pentagons in these fullerenes can be at an arbitrarily large distance from each other. IPR-fullerenes can be described as fullerenes in which each connected cluster of pentagons has size 1. In this paper we study the combinations of cluster sizes that can occur in fullerenes and whether the clusters can be at an arbitrarily large distance from each other. For each possible partition of the number 12, we are able to decide whether the partition describes the sizes of pentagon clusters in a possible fullerene, and state whether the different clusters can be at an arbitrarily large distance from each other. We will prove that all partitions with largest cluster of size 5 or less can occur in an infinite number of fullerenes with the clusters at an arbitrarily large distance of each other, that 9 partitions occur in only a finite number of fullerene isomers and that 15 partitions do not occur at all in fullerenes.     

Adherent and slippery walls for extrusion of entangled polymer melts and compounds

A brief overview is given of the distortions observed when polymer melts or compounds are extruded. It appears that extrusion through steel dies can be done either with macroscopic slip or with no-slip wall conditions. Recent experimental and theoretical progress made in understanding the various aspects of slip at the wall, and its measurement techniques, are presented. Boundary conditions for rubber compounds flowing through steel-walled dies could be seen to be much more complex than those for melts. However many aspects of the methodologies developed are of common interest both for melts and rubber. It has already been suggested that advantages can be obtained from the use of slippery walls in extrusion. Such wall properties have already been used indeed for a long time with compounds, where processing additives are introduced. New experimental data are presented concerning two typical EPDM compounds series, obtained using several laboratory techniques at the same time. Constitutive equations for the bulk and for friction at the wall can be introduced at present and adjusted to experimental data. Die extrusion can be simulated numerically, and significant improvements can be expected in quality and productivity.     

Extraction and spectrophotometric determination of ruthenium and osmium with thiobenzhydrazide

Ruthenium forms a pink complex with thiobenzhydrazide in hot 1.0-4.5M hydrochloric acid medium, which can be extracted with chloroform, and the extract shows maximal absorbance at 520 nm. The chloroform-extractable osmium-thiobenzhydrazide complex formed at pH 2.3-4.8 shows maximal absorption at 385 nm as well as at 480-490 nm. The colour of the extracts of both the complexes is stable for more than 24 hr and can be employed for the spectrophotometry of ruthenium and osmium in the presence of a considerable excess of diverse ions commonly associated with them. Ruthenium and osmium can be quantitatively separated from one another with thiobenzhydrazide.     

A Home-made Simple Set-up for Measurement of Electrochemical Surface Tension Spectrum on a Mercury Drop Electrode

A setup for recording surface tension curves at a mercury drop during potential scanning is designed based on photo-sensitive detection system. Surface tension spectrum at Hg drop can be recorded by voltammetric study. A Yb(III)-NO2- catalytic reduction system was used for characterization. The simple, sensitive technique can be expected to provide fresh information on molecular interactions at electrode surfaces.     

Kinetics of styrene polymerization at ultrahigh conversion

The radical-initiated bulk polymerization of styrene at low conversion can be adequately described by a simple kinetic scheme that involves initiation by the decomposition of a radical initiator, propagation, and termination by combination of polystyryl radicals. An integrated equation can be derived that will describe the relationship between monomer concentration and time. We have investigated the validity of applying equations of this kind in the 98–99.999% conversion range. From our experimental work we conclude that the initial rates at 130°C, when starting the polymerization at that temperature at more than 98% conversion, can be described by an integrated equation over at least two decades of monomer concentration. Deviations from the simple kinetics at ultrahigh conversion were observed after a certain time at 130°C. These are discussed and explained in terms of the kinetic assumptions made and an extended model is suggested to allow for depolymerization reactions that cannot be neglected at ultrahigh conversion.     

活性镁及活性氢化镁的合成

研究了在真空下90-150℃间使蒽镁分解生成高活性镁. 再常压加氢, 制得氢化镁的方法. 这一过程中, 镁的活化可循环使用蒽, 基本上不消耗任何试剂, 在分解前用过渡金属化合物掺杂到蒽镁中去可改善活化镁的氢化行为. 当蒽镁中掺杂5%的Cp2TiCl2时, 吸氢温度可降至90℃.