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研究了铌掺杂的Li/MgO甲烷氧化偶联催化剂的反应性质及铌的助剂作用。铌的引入使得该催化剂上甲烷氧化偶联反应的活化温度降低50℃以上, 使此温度降到了催化剂中碳酸锂的熔点附近。试验观察到部分催化剂上甲烷氧化偶联反应的活性曲线在碳酸锂的熔点附近有一转折, 这一转折现象的出现与否及程度取决于制备条件。在碳酸锂的熔点附近, 含有铌的催化剂得到活化, 观察到无稀释气体时的反应引燃现象, 即温度增加几度活性便达到最大值。当在比碳酸锂熔点稍高的温度下且不稀释时反应, 含铌催化剂活性很高但很快失活, 在稍低于此熔点下则不失活, 但活性较低。这些试验结果表明, 含铌催化剂的活化与失活均与催化剂中的碳酸锂的相变化有关。试验还观察到了在稍高于碳酸锂的熔点下做寿命试验时, 甲烷氧化偶联反应的振荡现象。 相似文献
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“铁丝在氧气中燃烧”是初中化学教材中证明氧气化学性质的一个演示实验,该实验证明了氧气比较活泼,在一定条件下可以和金属发生剧烈反应。但是与木炭在氧气中燃烧、硫在氧气中燃烧、蜡烛在氧气中燃烧的演示实验相比,铁丝在氧气中燃烧的实验存在着一些不足的地方,针对这些不足,对铁丝在氧气中燃烧的实验进行了改进。1实验存在的问题按照教材要求,铁丝在氧气中燃烧的实验,须将铁丝绕成螺旋状,并在铁丝的末端绑上一根火柴杆,实验时先将火柴杆点燃,待火柴杆将燃尽时,迅速伸入盛满氧气的集气瓶中。这样的操作存在2个问题:第一,火柴燃烧的程度不… 相似文献
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提高纤维素酶水解效率和降低水解成本 总被引:4,自引:0,他引:4
在我国可大量转化乙醇的是纤维质材料.纤维质材料转化乙醇的关键问题是纤维质转化为糖的过程,提高纤维素酶转化效率的方法有:(1)对纤维质材料进行预处理;(2)研究纤维素酶的最适作用条件;(3)纤维素酶的重复利用;(4)合理的发酵工艺等.本文分析了纤维素的结构以及纤维素酶的作用方式,总结了目前研究较多的几种纤维质材料预处理方法,及其对纤维素酶水解率的影响,并对研究纤维素酶的最适作用条件、纤维素酶的重复利用以及合理的发酵工艺进行了综述和分析. 相似文献
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当前,环境问题和能源危机已经威胁到人类的健康和生存。用于环境治理和化学能源合成新概念的纳米催化材料越来越受到人们的关注。催化作为一个特殊的纳米现象,是纳米材料应用领域的一个重要方向,在环境净化、能量转化和新化学品的生产等方面具有广泛的应用前景。早期的一氧化碳(CO)催化氧化研究主要集中在催化剂的制备方法以及制备条件对催化反应的影响等方面。本文针对CO催化氧化这一基础课题,以影响CO催化氧化的关键因素(如金属颗粒的大小,金属与载体之间的相互作用以及载体本身的作用等)为主线,简要概述了近年来CO催化氧化的催化机理及相关催化剂的最新研究进展。同时,结合我们课题组的一些最新研究结果,进一步指出了纳米材料在CO催化氧化方面还存在的一些值得关注的问题,并对未来CO氧化催化剂的研究做出展望,提出一些可行的研究方向。 相似文献
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《高分子通报》编辑部 《高分子通报》2008,(7)
《高分子通报》是1988年10月创刊的。回顾20年来的发展历程,《高分子通报》是在各级领导的关怀下不断成长的,是在我国高分子科学领域的专家、学者的大力支持下发展的,也是在历届编委、编辑艰苦奋斗,辛勤耕耘下不断提高和前进的。早在1981年冬,昆明功能高分子学术会议中就正式提 相似文献
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《Spectrochimica Acta Part B: Atomic Spectroscopy》1986,41(9):925-934
Three key characteristics with respect to quantitative performance: signal-to-noise ratio, matrix effects and analytical curve linearity, have been evaluated for mixed gas ICPs. The signal-to-noise ratio of CaII 393.3 was measured for argon and several mixed gas plasmas at a wide range of plasma powers, aerosol flow rates and observation heights. The data indicates that superior signal-to-noise ratios can, in general, be obtained for calcium with mixed gas ICPs when compared to a conventional Ar-ICP. In addition classic vaporization and easily ionizable element matrix effects are minimal in mixed gas ICPs even when low observation heights are utilized and analytical curves appear to retain the same linearity in mixed gas ICPs as those obtained using conventional Ar plasmas. 相似文献
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将银旋转圆盘电极在给定时间内浸在漂白液中进行氧化。在氧化过程中,来自漂白液中的卤化物在银电极表面与氧化生成的银离子形成卤化银。氧化反应生成的卤化银量可以用电化学还原方法进行定量测定。利用这种简单的方法可以研究漂白动力学,研究漂白液的组份、浓度和pH对漂白速度的影响。通过记录在银电极上氧化还原对的电流。电位曲线可以定量描述漂白过程。 相似文献
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尼龙1010环状球晶的研究 总被引:4,自引:0,他引:4
利用偏光显微镜研究了尼龙1010环状球晶的生成条件、形态特征和光学性质,发现在等温结晶过程中只可生成环状球晶;在降温过程中可由相同光性的放射状球晶转变成正、负、混合光性环状球晶;在升温过程中正光性和混合光性环状球晶分别转变成不对称四瓣形和六瓣形环状球晶,负放射球晶可转变成另一种负环状球晶。 相似文献
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IntroductionReversiblecolorchangesuponexternalorinternalstimulationshavebeenattractingmuchattentionduetotheirutilityasfunctionalmaterials .Forexample ,pho tochromismdescribesthecolorchangesinducedbypho toirradiationandcanbeusedasphoto recordingmateri als… 相似文献
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Li H Han B Liu J Gao L Hou Z Jiang T Liu Z Zhang X He J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(24):5593-5600
The effects of pressure and of the composition of the CO2/ethanol mixed solvent in the critical region on the kinetics of the decomposition of 2,2'-azobis(isobutyronitrile) (AIBN) were studied at 333.15 K. The rate constants (kd) in the mixed solvent far from the critical point and in liquid n-hexane and ethanol were also determined for comparison. It was found that kd is very sensitive to pressure in the mixed solvent near the critical point. However, in the mixed solvent outside the critical region kd is nearly independent of pressure. Interestingly, kd in the mixed solvent in the critical region can be higher than that in ethanol at the same temperature, suggesting that no significant enhancement in the reaction rate by a small pressure change in the critical region of the mixed solvent can be achieved by changing the composition of the liquid solvent in the traditional way. Transition-state theory can predict kd in the mixed solvent far from the critical point and in the liquid solvents well. However, it cannot predict kd in the mixed solvent in the critical region. The special intermolecular interaction between the solvent and the reaction species may contribute to this interesting phenomenon. This work also shows that if pure CO2 or ethanol are used as solvents, the reaction cannot be carried out in the critical region of the solvents at the desired temperature, while it can be conducted in the critical region of the mixed solvent of suitable composition, where the solvent is highly compressible. 相似文献
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Wang B Han B Jiang T Zhang Z Xie Y Li W Wu W 《The journal of physical chemistry. B》2005,109(50):24203-24210
The reaction rate of the Diels-Alder reaction between N-ethylmaleimide and 9-hydroxymethylanthrance in CO2 + ethanol and CO2 + hexane mixed solvents of different compositions were determined by in situ UV/vis spectroscopy at 318.15 K and different pressures. The density of the mixed solvents at different pressures was also determined and the isothermal compressibility was calculated using the density data. The activation volume of the reaction was calculated based on the dependence of rate constant (kc) on pressure. It was demonstrated that the kc was very sensitive to the pressure in the mixed solvents near the critical region and the kc increased dramatically as pressure approached dew points, critical point, and bubble points of the mixed solvents. However, the kc in the mixed solvents outside the critical region or in pure CO2 was not sensitive to pressure. At suitable conditions, kc could be 40 times larger than that in acetonitrile. The activation volume of the reaction was nearly independent of pressure as the pressure was much higher than the phase separation pressure of the mixed solvents, while it increased considerably as pressure approached the bubble points, critical point, and dew points from high pressure. The clustering of the solvent molecules with the reactants and the activated complex in the reaction systems near the phase boundary in the critical region may be the main reason for the interesting phenomena observed. This work also shows that, using pure CO2 as the solvent, the reaction cannot be carried out in the critical region of the solvent due to the limitations of the reactants, while it can be conducted in the critical region of mixed solvents of suitable compositions, where the solvents are highly compressible and the reaction rate can be tuned effectively by pressure. 相似文献
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In this work, we develop a new algorithm for nonequilibrium molecular dynamics of fluids under planar mixed flow, a linear combination of planar elongational flow and planar Couette flow. To date, the only way of simulating mixed flow using nonequilibrium molecular dynamics techniques was to impose onto the simulation box irreversible transformations. This would bring the simulation to an end as soon as the minimum lattice space requirements were violated. In practical terms, this meant repeating the short simulations to improve statistics and extending the box dimensions to increase the total simulation time. Our method, similar to what has already been done for pure elongational flow, allows a cuboid box to deform in time following the streamlines of the mixed flow and, after a period of time determined by the elongational field, to be mapped back and recover its initial shape. No discontinuity in physical properties is present during the mapping and the simulation can, in this way, be extended indefinitely. We also show that the most general form of mixed flow, in which the angle between the expanding (or contracting) direction and the velocity gradient axis varies, can be cast in a so-called canonical form, in which the angle assumes values that are multiples of π (when a mixed flow exists), by an appropriate choice of the field parameters. 相似文献
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分子间弱相互作用热力学研究的直接实验方法就是利用量热手段测定相互作用的能量参数. 本文对TAM III-ITC 纳焦级量热计进行了电标定实验和标准反应热测量, 结果显示本量热计的精密度为±0.09%; 量热用基准物质三羟甲基氨基甲烷(Tris)与盐酸的反应热((-47.48±0.12) kJ·mol-1)与文献值一致. 采用此量热计,对典型的头-尾链型阳离子表面活性剂十二烷基三甲基溴化铵(DTAB)测量得到了与文献报导值很好吻合的临界胶束浓度(cmc)和胶束化焓, 而且对具有亲水-疏水面式刚性结构的生物表面活性剂胆酸钠(NaC)也获得了可靠的结果. 进一步地, 对于相反电荷的混合表面活性剂体系(DTAB/NaC), 分别研究了在富NaC区和富DTAB区体系混合胶束的形成. 结果说明DTAB/NaC混合表面活性剂体系在富NaC区有较强的协同效应, 而在富DTAB区的协同效应较弱. 本文结合电导率测定结果, 对DTAB/NaC混合体系在水溶液中的分子自组装热力学行为进行了有价值的讨论. 相似文献
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Kazuo Tanaka Fumiyasu Ishiguro Tomoyuki Kunita Yoshiki Chujo 《Journal of polymer science. Part A, Polymer chemistry》2009,47(23):6441-6450
We report the facile preparation of the conductive polymer composites containing the mixed‐valence tetrathiafulvalene (TTF) nanofibers and their applications as all‐organic transparent conductive materials. TTF can be used as a nanofiller for transforming conventional polymers to conductive materials. Self‐assemble nanofibers of the neutral and radical cation of TTF can be formed in the polymer solutions during the film deposition, and the resulting composite films with several micron thickness can serve as the conductive material with high transparency. Several kinds of conventional polymers, such as polystyrene, poly(methyl methacrylate) (PMMA), and poly(vinylpyrrolidone), can be used as a polymer matrix of the composites. The conductivities of the PMMA film containing 35 mol % of the mixed‐valence TTF and the PEDOT–PSS film showed similar values (2.8 × 10–2 and 5.4 × 10–1 S/cm, respectively). In contrast, the normalized transmittance of the PMMA film by 1‐μm thickness greatly increased (96%/μm) when compared with that of the PEDOT–PSS film (10%/μm). In addition, the degradation of the conductivity of the nanofibers by heating and aging was effectively suppressed in the composite samples. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6441–6450, 2009 相似文献